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Background: The ligaments and soft tissue capsular structures of the knee joint that provide a resisting force to prevent abnormal knee hyperextension have not been determined. This knowledge is required for the diagnosis and treatment of knee hyperextension abnormalities. Purpose: To determine the resisting moment of knee ligament and capsular structures that resist knee hyperextension. Hypothesis: The combined posteromedial and posterolateral capsular structures function to provide a major restraint to prevent abnormal knee hyperextension. The anterior and posterior cruciate ligaments resist knee hyperextension but function as secondary restraints. Study Design: Descriptive laboratory study. Methods: A 6 degrees of freedom robotic system determined intact laxity limits in 24 cadaveric knees from 0° to 100° of knee flexion for anteroposterior limits at ±135 N, abduction-adduction limits at ±7 N·m, and external-internal limits at ±5 N·m. One loading method (n = 14 knees) used a static loading sequence with knee hyperextension to 27-N·m torque while maintaining all other degrees of freedom at zero load during sequential soft tissue cutting. The second method (n = 10 knees) used a cyclic loading sequence to decrease viscoelastic effects with soft tissue cutting at 0° of extension, followed by knee hyperextension to 27-N·m torque and cycled back to 0°. Selective soft tissue cuttings were performed of the following: oblique popliteal ligament, fabellofibular ligament, posterolateral capsule, posteromedial capsule with posterior oblique ligament, cruciate ligaments, lateral collateral ligament, popliteus, anterolateral ligament and iliotibial band, and superficial plus deep medial collateral ligaments. The sequential loss in the restraining moment with sectioning provides the function of that structure in resisting knee hyperextension. Results: The median resisting force to knee hyperextension, in descending order, was the posteromedial capsule and posterior oblique ligament (21.7%), posterorolateral ligament and fabellofibular ligament (17.1%), anterior and posterior cruciate ligaments (13% and 12.9%, respectively), superior and deep medial collateral ligament (9.6%), oblique popliteal ligament (7.7%), and lateral collateral ligament (5.4%). The combined posterior capsular structures provided 54.7% and the anterior and posterior cruciate ligaments 25.3% of the total resisting moment to prevent knee hyperextension. Conclusion: Diagnosis of abnormal knee hyperextension involves a combination of multiple ligament and soft tissue structures without 1 primary restraint. The posteromedial and posterolateral capsular structures provided the major resisting moment to prevent knee hyperextension. The cruciate ligaments produced a lesser resisting moment to knee hyperextension. Clinical Relevance: This is the first study to comprehensively measure all of the knee ligaments and capsular structures providing a resisting moment to abnormal knee hyperextension. These data are required for diagnostic and treatment strategies on the pathomechanics of abnormal knee hyperextension in patients after injury or developmental cases.

Purpose To report a prospective study of patients who underwent blood flow restriction training (BFRT) for marked quadriceps or hamstring muscle deficits after failure to respond to traditional rehabilitation after knee surgery. Methods The BFRT protocol consisted of 4 low resistance exercises (30% of 1 repetition maximum): leg press, knee extension, mini-squats, and hamstring curls with 60% to 80% limb arterial occlusion pressure. Knee peak isometric muscle torque (60° flexion) was measured on an isokinetic dynamometer. Results Twenty-seven patients (18 females, 9 males; mean age, 40.1 years) with severe quadriceps and/or hamstrings deficits were enrolled from April 2017 to January 2020. They had undergone a mean of 5.3 ± 3.5 months of outpatient therapy and 22 ± 10 supervised therapy visits and did not respond to traditional rehabilitation. Prior surgery included anterior cruciate ligament reconstruction, partial or total knee replacements, meniscus repairs, and others. All patients completed 9 BFRT sessions, and 14 patients completed 18 sessions. The mean quadriceps and hamstrings torque deficits before BFRT were 43% ± 16% and 38% ± 14%, respectively. After 9 BFRT sessions, statistically significant improvements were found in muscle peak torque deficits for the quadriceps (P = .003) and hamstring (P = .02), with continued improvements after 18 sessions (P = .004 and P = .002, respectively). After 18 BFRT sessions, the peak quadriceps and hamstring peak torques increased > 20% in 86% and 76% of the patients, respectively. The failure rate of achieving this improvement in peak quadriceps and hamstring torque after 18 BFRT sessions was 14% and 24%, respectively. Conclusions BFRT produced statistically significant improvements in peak quadriceps and hamstring torque measurements after 9 and 18 sessions in a majority of patients with severe quadriceps and hamstring strength deficits that had failed to respond to many months of standard and monitored postoperative rehabilitation. Level of Evidence Level IV therapeutic case series.

Purpose To determine the statistical and predictive correlation between instrumented Lachman and pivot-shift tests with progressive loss of anterior cruciate ligament (ACL) function. Methods The kinematic correlations between pivot-shift and Lachman anterior tibial translations (ATTs) in ACL-deficient and ACL-reconstructed states and in partially lax ACL grafts were determined with precise robotic testing in cadaveric knees. The Lachman test (100-N anteroposterior) and 2 pivot-shift loadings were conducted: anterior tibial loading (100 N), valgus rotation (7 Nm), and internal rotation (5 Nm and 1 Nm). The tibia was digitized to study the resulting medial, central, and lateral tibiofemoral compartment translations. In group 1 knees, 15 bone–patellar tendon–bone reconstructions were first tested, followed by ACL graft loosening with 3- and 5-mm increases in Lachman ATT. In group 2, 43 knees underwent robotic testing before and after ACL sectioning and underwent analysis of the effect of 3- and 5-mm increases in Lachman ATT and complete ACL sectioning on pivot-shift compartment translations. Results In group 1 knees, ACL graft loosening allowing a 3-mm increase in Lachman ATT resulted in increases in pivot-shift lateral compartment translation (lateral compartment ATT) of only 1.6 ± 0.3 mm and 2.2 ± 1.0 mm (internal rotation of 5 Nm and 1 Nm, respectively) that were one-half of those required for a positive pivot-shift test finding. In group 2, for a 3-mm increased Lachman test, there were no positive pivot-shift values. In both groups, a Lachman test with an increase in ATT of 3 mm or less (100 N) had a 100% predictive value for a negative pivot-shift test finding. With ACL graft loosening and a 5-mm increase in the Lachman ATT, group 1 still had no positive pivot-shift values, and in group 2, a positive pivot-shift test finding occurred in 3 of 43 knees (7%, pivot shift 1-Nm internal rotation). After ACL sectioning, a highly predictive correlation was found between abnormal increases in Lachman and pivot-shift translations (P Conclusions ACL graft slackening and an instrumented Lachman test with an increase in ATT of 3 mm or less were 100% predictive of a negative pivot-shift subluxation finding and retained ACL stability. Further graft slackening and a 5-mm increase in the Lachman ATT produced pivot-shift lateral compartment ATT increases still less than the values in the ACL-deficient state; however, 7% of the knees (3 of 43) were converted to a positive pivot-shift test finding indicative of ACL graft failure. Clinical Relevance Instrumented Lachman tests provide objective data on ACL function and graft failure to supplement subjective pivot-shift tests and are highly recommended for single-center and multicenter ACL studies. In the past decade, a near majority of published ACL studies no longer reported on instrumented Lachman tests, relying solely on highly subjective pivot-shift grading by multiple examiners.

The altered knee joint function and symptomatic state in younger patients after meniscectomy and progressive tibiofemoral arthritis remain an important unsolved treatment dilemma. Meniscal allograft transplantation has evolved as an acceptable treatment because there are few (if any) other options. The procedure is effective in most patients, who experience a decrease in tibiofemoral pain and improved knee function, even allowing a return to light recreational activities. However, biological remodeling of the implant occurs over time, with replacement of the complex circumferential and radial fibers with disorganized collagen tissues and altered cellular and proteoglycan components that affects load bearing and negates chondroprotective function. Positive patient outcomes may still be reported even with the loss of meniscal transplant function on magnetic resonance imaging giving a false-positive survivorship analysis. Repeated surgical procedures are frequent by 10 years. Patients are advised that meniscal allograft transplant surgery, although beneficial in the short term to buy time, is not curative.

This is the second of two chapters that detail our total knee arthroplasty (TKA) postoperative rehabilitation program, whose overall goal is to return patients to an active lifestyle to enhance their overall quality of life. Chapter 6 provides details for the first 12 postoperative weeks that restore sufficient muscle strength to allow pain-free activities of daily living as well as return to light work and low-impact aerobic activities such as walking, bicycling, and swimming. Because TKA is performed in many younger patients, the desire to return to recreational sports activities is important to these individuals. In our experience, additional strengthening and conditioning exercises are usually required in order to safely prepare them to participate in activities such as doubles tennis, light jogging, hiking, and skiing. Patients are counseled to perform these activities in a light or less strenuous manner to protect the knee joint and decrease the risk of prosthetic loosening that may occur with strenuous or higher-impact activities. The rehabilitation program is detailed here, along with precautions to avoid recurrent symptoms of knee pain and swelling that can prolong the course to complete recovery. Our return-to-recreational-sports criteria are provided, which include several objective tests to measure strength and function. Data are provided from our clinical studies to show the effectiveness of our program.

This is the first of two chapters that detail our total knee arthroplasty (TKA) postoperative rehabilitation program, whose overall goal is to return patients to an active lifestyle without pain or complaints of knee joint stability to enhance their overall satisfaction and quality of life. The goals in the first 12 postoperative weeks are to resolve pain and swelling and restore adequate range of knee motion (ROM), gait, and balance. Our rehabilitation protocol is described in detail and includes the use of modalities and progression for ROM, weight-bearing, strength, balance, and aerobic conditioning. This program is effective in restoring sufficient muscle strength to allow pain-free activities of daily living as well as return to light work and low-impact aerobic activities such as walking, bicycling, and swimming. Chapter 7 provides additional rehabilitation recommendations for strengthening and aerobic conditioning for patients desiring to return to sports and other more strenuous physical activities, as well as our return to activity testing guidelines.

Total knee arthroplasty (TKA) is one of the most commonly performed elective surgical procedures in the USA, with an exponential growth in volume noted in the past few decades. Many studies have provided estimated future projections of TKA volume and incidence rates using different epidemiological models. Incidence rates are typically calculated as the number of TKAs during a specified time period divided by the size of the US population (using US Census Bureau data) during the same time period. This chapter assesses the most current data available as of May 2020 and discusses factors that affect models and projections for future TKA numbers in the USA. Factors such as age and gender are taken into account when available. The effect of long-term participation in athletics and sports injuries on the future development of knee osteoarthritis and potentially TKA is reviewed.

The determination of outcome after knee arthroplasty requires assessment of both patient-reported outcome measures (PROMs) and objective parameters that measure strength, balance, and functional performance. This chapter details the most commonly used PROMs and provides reliability, validity, responsiveness, minimal clinically important difference (MCID), and minimally important change (MIC) when possible to assist users in understanding these instruments. The PROMs include the Knee Society Scoring System, WOMAC, Knee Injury and Osteoarthritis Outcome Score (KOOS), KOOS Joint Replacement Survey (KOOS JR), Short Form-36 and Short Form-12, and PROMIS Global-10 Short Form. Activity rating scoring systems typically used after knee arthroplasty are also provided.

Unicompartmental knee arthroplasty (UKA) is a valid treatment option for patients in whom severe joint damage and complete loss of joint space are present in one compartment. The primary indication is symptomatic isolated painful arthritis marked by moderate to severe joint line pain and/or stiffness that limits daily activities. Preexisting joint arthritis in another compartment of the knee is the principal contraindication because of the noteworthy evidence that this is the leading cause of failure. Robotic-assisted surgical navigation improves accuracy in UKA (postoperative limb alignment, component positioning, and soft tissue balancing) using less invasive techniques. The UKA operative technique described in this chapter uses an implant that is positioned using three-dimensional modeling and computer-assisted robotic surgical navigation. It is important that the patient has realistic expectations regarding what this operation may and may not accomplish. Low-impact activities such as walking, swimming, golfing, light hiking, and bicycling can often be performed by 3 months. Running and high-impact athletic or occupational activities are not advised. Ten-year survivorship rates range from 81% to 98% for medial UKA and from 83% to 92% for lateral UKA.

This chapter discusses the effect of nutritional deficiencies and obesity on outcomes of total knee arthroplasty (TKA) and provides the rationale for testing and preoperative intervention to reduce their potentially deleterious effects. Many studies have provided evidence that preoperative malnutrition (albumin level < 3.5 dg/L) leads to poorer postoperative outcomes and increased complication rates after primary TKA. In addition, several investigations have reported that obesity is associated with increased rates of postoperative infection and other major complications. Strategies to improve nutritional levels and lower body weight exist, including bariatric surgery; however, evidence remains low regarding which are the most effective and the timing of preoperative intervention necessary to significantly improve outcomes. The senior author’s patient indications and selection criteria are provided.

In order to determine the most important factors for achieving patient satisfaction and improving quality of life (QOL) following total knee arthroplasty (TKA), validated scales must be used and influences of compounding factors must be accounted for such as comorbidities, mental and emotional problems, and pain in other joints. Although a variety of scales and questions have been used to rate patient satisfaction, few have been validated and there is tremendous variation in recent literature regarding this topic. Conversely, QOL instruments have well-documented psychometric properties and historically have been used throughout the orthopedic literature. Many factors have been shown to be predictive of patient satisfaction, including meeting patient preoperative expectations and postoperative function and pain relief as shown by scores on the Knee Society and Oxford Knee Society scales. Factors predictive of patient dissatisfaction include the presence of two or more comorbidities, female gender, depression, and low preoperative scores on the Medial Outcomes Short Form 12 and Western Ontario and McMaster Universities Osteoarthritis Index instruments.

Total knee arthroplasty (TKA) is routinely performed in younger patients who desire to be active in fitness and recreational sports and enjoy the benefits of a healthy lifestyle. This chapter provides the most updated physical activity guidelines for adults from the American Heart Association. We performed an extensive literature review, and data are summarized from 21 studies that detailed recreational and sports activities patients participated in after TKA. This included types of activities, frequency of participation, and whether symptoms or limitations occurred for future patient counseling considerations. Details are provided for eight studies that used accelerometers to measure physical activity 6–12 months postoperatively, of which only three determined the percent of patients who achieved AHA recommended PA guidelines. Current recommendations for activities allowed after TKA from various orthopedic societies and a systematic review are included.

The determination of outcome after total knee arthroplasty (TKA) requires assessment of both patient-reported outcome measures and objective parameters that measure strength, balance, and functional performance. This chapter details the most common objective assessments used postoperatively in the standard clinic setting such as isometric muscle testing, Y-balance testing, timed walking, and chair standing testing. Reliability, validity, responsiveness, and normative data are provided. Several test batteries are also described that encompass multiple objective measurements to use for return to recreational or sports activities.

Background: Anterior cruciate ligament (ACL) graft conditioning protocols to decrease postoperative increases in anterior tibial translation and pivot-shift instability have not been established. Purpose: To determine what ACL graft conditioning protocols should be performed at surgery to decrease postoperative graft elongation after ACL reconstruction. Study Design: Controlled laboratory study. Methods: A 6 degrees of freedom robotic simulator evaluated 3 ACL graft constructs in 7 cadaver knees for a total of 19 graft specimens. Knees were tested before and after ACL sectioning and after ACL graft conditioning protocols before reconstruction. The ACL grafts consisted of a 6-strand semitendinosus-gracilis TightRope, bone–patellar tendon–bone TightRope, and bone–patellar tendon–bone with interference screws. Two graft conditioning protocols were used: (1) graft board tensioning (20 minutes, 80 N) and (2) cyclic conditioning (5°-120° of flexion, 90-N anterior tibial load) after graft reconstruction to determine the number of cycles needed to obtain a steady state with no graft elongation. After conditioning, the grafts were cycled a second time under anterior-posterior loading (100 N, 25° of flexion) and under pivot-shift loading (100 N anterior, 5-N·m internal rotation, 7 N·m valgus) to verify that the ACL flexion-extension conditioning protocol was effective. Results: Graft board tensioning did not produce a steady-state graft. Major increases in anterior tibial translation occurred in the flexion-extension graft-loading protocol at 25° of flexion (mean ± SD: semitendinosus-gracilis TightRope, 3.4 ± 1.1 mm; bone–patellar tendon–bone TightRope, 3.2 ± 1.0 mm; bone–patellar tendon–bone with interference screws, 2.4 ± 1.5 mm). The second method of graft conditioning (40 cycles, 5°-120° of flexion, 90-N anterior load) produced a stable conditioned state for all grafts, as the anterior translations of the anterior-posterior and pivot-shift cycles were statistically equivalent ( P < .05, 1-20 cycles). Conclusion: ACL graft board conditioning protocols are not effective, leading to deleterious ACL graft elongations after reconstruction. A secondary ACL graft conditioning protocol of 40 flexion-extension cycles under 90-N graft loading was required for a well-conditioned graft, preventing further elongation and restoring normal anterior-posterior and pivot-shift translations. Clinical Relevance: There is a combined need for graft board tensioning and robust cyclic ACL graft loading before final graft fixation to restore knee stability.

Purpose To investigate patients with generalized joint laxity (GJL) after primary anterior cruciate ligament reconstruction (ACLR) as to the risk of ACLR failure, graft selection success rates, and overall clinical outcomes. Methods A systematic review of the PubMed and EMBASE databases was performed to identify studies published from the inception of the databases through February 4, 2020. The inclusion criteria were original studies written in English involving outcomes of patients with GJL who had undergone primary ACLR. Results Nine studies met the inclusion criteria, which included 1,869 patients. Most underwent isolated bone–patellar tendon–bone (BPTB; n = 1062) or hamstring autograft (n = 696) ACLR. Overall, higher graft failure rates tended to occur in patients with GJL compared with patients without GJL (range per study: 6%-30% vs 0%-12.3%). Inferior results were also found patients with GJL in patient-reported outcome measures and postoperative knee stability determined by KT, Lachman, and pivot-shift tests. BPTB autografts tended to have lower failure rates than hamstring autografts in patients with GJL (range per study: 6%-21% vs 17.6%-30%). Only 1 study determined outcomes of a combined ACLR and extra-articular augmentation in patients with GJL. Conclusions Patients with GJL are at an increased risk of inferior outcomes and graft failure after primary ACLR. BPTB autografts may have more favorable stability outcomes compared with hamstring autografts in patients with GJL. However, the reported stability parameters and KT results, even with a BPTB autograft, remain inferior to non-GJL published results, and the added benefit of an extra-articular procedure to supplement the primary ACLR deserves consideration. Level of Evidence Level III, systematic review of Level II and III investigations.

Context:Anterior cruciate ligament (ACL) reconstruction (ACLR) is frequently performed in patients younger than 20 years whose goal is to return to sport (RTS). Varying reinjury rates have been reported, and the factors responsible are unclear. Studies differ with regard to age, graft type, surgical techniques, postoperative rehabilitation, RTS guidelines, and methods used to determine ACL failures.Objective:To determine RTS rates; the effect of participation in high-risk sports, sex, and graft type on ACL reinjury rates; and whether objective test criteria before RTS correlate with lower reinjury rates.Data Sources:A systematic review of the literature from inception to May 31, 2019, was conducted using the PubMed and Cochrane databases.Study Selection:Studies on transphyseal ACLR in athletes Study Design:Systematic review.Level of Evidence:Level 4.Results:A total of 1239 patients in 8 studies were included; 87% returned to sport and 80% resumed high-risk activities. Of the patients, 18% reinjured the ACL graft and/or the contralateral ACL. Nine percent of patellar tendon autografts and 15% of hamstring autografts failed (odds ratio [OR], 0.52; P = 0.002). Of reinjuries, 90% occurred during high-risk sports. Male patients had a significantly higher rate of ACL graft failure than female patients (OR, 1.64; P = 0.01). There was no sex-based effect on contralateral ACL injuries. Only 1 study cited objective criteria for RTS.Conclusion:A high percentage of athletes returned to sport, but 1 in 5 suffered reinjuries to either knee. Male patients were more likely to reinjure the ACL graft. Objective criteria for RTS were rarely mentioned or not detailed. The need for testing of knee stability, strength, neuromuscular control, agility, and psychological measures before RTS remains paramount in young athletes.

A high tibial osteotomy (HTO) that is used to correct varus malalignment, such as with medial arthrosis or before cartilage restoration or posterolateral reconstructions, represents an important and required surgery for clinical success. A major problem that occurs with HTO planning is that the preoperative measurements, with either lower limb supine or standing weight-bearing radiographs, will invariably show abnormal medial or lateral tibiofemoral compartment opening resulting from soft-tissue laxity or injury. It is imperative that this tibiofemoral joint opening be accounted for in the osteotomy correction calculations. There are well-described methods available that affect operative planning, such as the use of preoperative stress radiographs to determine the millimeters of tibiofemoral opening or closure. The use of intraoperative fluoroscopy with application of axial loading to the lower limb and verification of closure of the tibiofemoral joint is recommended. A careful fluoroscopic examination of the tibiofemoral compartments allows a final adjustment of the osteotomy correction and confirms the final weight-bearing line percent measurement and limb alignment. Postoperative radiographs are required to detect outliers resulting from unexpected soft-tissue laxity or inadequate correction.

Background The effect of an anterior cruciate ligament (ACL) reconstruction on restoring normal knee kinematics in unstable knees with physiologic laxity of secondary ligamentous restraints remains unknown. The purpose of this study was to determine the stabilizing function of an ACL reconstruction and the resulting ACL graft forces in knees with severely abnormal anterior subluxation due to associated laxity of secondary restraints. Methods A 6-degree-of-freedom robotic simulator was used to test 21 cadaveric knees studied as a whole and in subgroups of lax secondary restraints (Lax-SR) and intact secondary restraints (Intact-SR), based on abnormal translations and tibial rotations. Native, ACL-sectioned, and ACL-reconstructed conditions were tested. An instrumented bone-patellar tendon-bone (BPTB) graft measured ACL graft forces. The loading profile involved the Lachman test (25° of flexion and 100-N anterior load), anterior tibial loading (100-N anterior load across 10° to 90° of flexion), internal rotation (25° of flexion and 5-Nm torque), and 2 pivot-shift simulations (100-N anterior load, 7-Nm valgus, and either 5 Nm of internal rotation [Pivot Shift 1] or 1 Nm of internal rotation [Pivot Shift 2]). Equivalence between conditions was defined as being within 2 mm for compartment translation and within 2° for internal tibial rotation, with p Results ACL sectioning increased center translation in the Lachman test by a mean of 10.9 mm (95% confidence interval [CI], 9.3 to 12.5 mm; p = 0.99), which was equivalent to native values after ACL reconstruction in all knees (mean difference, 0.0 mm [95% CI, -0.4 to 0.4 mm]; p = 0.0013), and in subgroups of Lax-SR (mean difference, 0.2 mm [95% CI, -0.5 to 0.8 mm]; p = 0.03) and Intact-SR (mean difference, -0.2 mm [95% CI, -0.8 to 0.4 mm]; p = 0.002). ACL sectioning in the pivot-shift (5-Nm) test increased lateral compartment translation to non-native-equivalent levels, which were restored to native-equivalent values after ACL reconstruction in all knees (mean difference, 0.9 mm [95% CI, 0.4 to 1.4 mm]; p = 0.055), in the Intact-SR subgroup (mean difference, 1.1 mm [95% CI, 0.5 to 1.8 mm]; p = 0.03), and to nearly native-equivalence in the Lax-SR subgroup (mean difference, 0.6 mm [95% CI, -0.3 to 1.6 mm; p = 0.06). The highest ACL graft force reached a mean of 190.9 N in the pivot-shift (5-Nm) test. Conclusions The ACL reconstruction restored native kinematics and native rotational stability in all knees, including knees having laxity of secondary ligamentous restraints and clinically equivalent Grade-3 pivot-shift subluxation, and did so at ACL graft forces that were not excessive. Clinical relevance An ACL reconstruction with a BPTB graft restored normal stability parameters regardless of the integrity of secondary ligamentous restraints.

Background: Approximately two-thirds of anterior cruciate ligament (ACL) tears are sustained during noncontact situations when an athlete is cutting, pivoting, decelerating, or landing from a jump. Some investigators have postulated that fatigue may result in deleterious alterations in lower limb biomechanics during these activities that could increase the risk of noncontact ACL injuries. However, prior studies have noted a wide variation in fatigue protocols, athletic tasks studied, and effects of fatigue on lower limb kinetics and kinematics. Purpose: First, to determine if fatigue uniformly alters lower limb biomechanics during athletic tasks that are associated with noncontact ACL injuries. Second, to determine if changes should be made in ACL injury prevention training programs to alter the deleterious effects of fatigue on lower limb kinetics and kinematics. Study Design: Systematic review; Level of evidence, 4. Methods: A systematic review of the literature using MEDLINE was performed. Key terms were fatigue, neuromuscular, exercise, hop test, and single-legged function tests. Inclusion criteria were original research studies involving healthy participants, use of a fatigue protocol, study of at least 1 lower limb task that involved landing from a hop or jump or cutting, and analysis of at least 1 biomechanical variable. Results: Thirty-seven studies involving 806 athletes (485 female, 321 male; mean age, 22.7 years) met the inclusion criteria. General fatigue protocols were used in 20 investigations, peripheral protocols were used in 17 studies, and 21 different athletic tasks were studied (13 single-legged, 8 double-legged). There was no consistency among investigations regarding the effects of fatigue on hip, knee, or ankle joint angles and moments or surface electromyography muscle activation patterns. The fatigue protocols typically did not produce statistically significant changes in ground-reaction forces. Conclusion: Published fatigue protocols did not uniformly produce alterations in lower limb neuromuscular factors that heighten the risk of noncontact ACL injuries. Therefore, justification does not currently exist for major changes in ACL injury prevention training programs to account for potential fatigue effects. However, the effect of fatigue related to ACL injuries is worthy of further investigation, including the refinement of protocols and methods of analysis.

To determine the stabilizing effect of the anterolateral ligament (ALL) and iliotibial band (ITB) in resisting internal tibial rotation limits and anterior subluxations of the tibiofemoral compartments in anterior cruciate ligament (ACL)-intact knees during anterior drawer, internal rotation, and under 2 different 4-degree-of-freedom pivot-shift conditions.A 6-degree-of-freedom robotic simulator tested 19 fresh-frozen cadaver specimens with 3 testing conditions: intact, ALL- or ITB-sectioned (random), and both ALL and ITB sectioned. Anterior translation of the medial and lateral compartments and internal tibial rotation were measured under 100 N anterior drawer, 5 Nm internal rotation, and 2 pivot-shift conditions. Statistical equivalence was defined as P.05.Sectioning the ALL alone had no effect on lateral compartment translation or internal rotation under any loading condition (equivalent P.05). After ITB sectioning alone, small increases in internal rotation were found under 5 Nm internal rotation at 60° (3.0° [90% confidence interval 1.9-4.1]; P = .99) and 90° (2.2° [90% confidence interval 1.5-2.9]; P = .84) flexion. After both ALL and ITB were sectioned, increases in internal rotation of 1.7°, 4.5°, and 3.9° occurred at 25°, 60°, and 90° flexion, respectively (P.05). Small increases in pivot-shift internal rotation (Group 1: 2.0° [90% confidence interval 1.4-2.6]; P = .52) and lateral compartment translation occurred (Group 1: 0.9 mm [90% confidence interval 0.7-1.1]; P.001).Sectioning the ALL does not lead to an increase in tibiofemoral compartment subluxations in the pivot-shift test with an intact ACL. Accordingly the ALL would not represent a primary restraint to pivot-shift subluxations. ALL sectioning alone does not lead to an increase in internal rotation motion limits, however sectioning both the ALL and ITB did produce small increases in rotation limits at higher flexion angles which would likely not be clinically detectable.A deficiency to both the ALL and ITB during in vitro-simulated pivot-shift tests and internal rotation tests results in small, clinically undetectable changes in knee kinematics in the majority of knees assuming intact ACL function.

The purpose of this study was to perform an evidence-based, expert consensus survey using the Delphi panel methodology to develop recommendations for the treatment of degenerative meniscus tears.Twenty panel members were asked to respond to 10 open-ended questions in rounds 1 and 2. The results of the first 2 rounds served to develop a Likert-style questionnaire for round 3. In round 4, the panel members outside consensus were contacted and asked to either change their score in view of the group's response or argue their case. The level of agreement for round 4 was defined as 80%.There was 100% agreement on the following items: insidious onset, physiological part of aging, tears often multiplanar, not all tears cause symptoms, outcomes depend on degree of osteoarthritis, obesity is a predictor of poor outcome, and younger patients (50 years) have better outcomes. There was between 90% and 100% agreement on the following items: tears are nontraumatic, radiographs should be weightbearing, initial treatment should be conservative, platelet-rich plasma is not a good option, repairable and peripheral tears should be repaired, microfracture is not a good option for chondral defects, the majority of patients obtain significant improvement and decrease in pain with surgery but results are variable, short-term symptoms have better outcomes, and malalignment and root tears have poor outcomes.This consensus statement agreed that degenerative meniscus tears are a normal part of aging. Not all tears cause symptoms and, when symptomatic, they should initially be treated nonoperatively. Repairable tears should be repaired. The outcome of arthroscopic partial meniscectomy depends on the degree of osteoarthritis, the character of the meniscus lesion, the degree of loss of joint space, the amount of malalignment, and obesity. The majority of patients had significant improvement, but younger patients and patients with short-term symptoms have better outcomes.Level V - expert opinion.

This chapter describes training techniques essential for return to competitive tennis after major knee injury or surgery. Exercises and drills designed to improve dynamic balance, agility, speed, strength, and aerobic conditioning are illustrated and described in detail. Field tests are described that measure lower extremity power and dynamic balance, upper body strength and power, speed and agility, abdominal strength and endurance, and aerobic fitness. Reference material for training elite national and international players is given, along with normative data regarding strength, power, speed, agility, and aerobic fitness. The authors’ program, Sportsmetrics tennis, was found to be safe and effective in improving neuromuscular indices and athletic performance indicators in youth players and is recommended as end-stage rehabilitation after a knee injury or surgery before return to competitive play.

This chapter summarizes return to sport (RTS) data from 52 studies involving 10,192 patients who underwent either unicompartmental tibiofemoral knee arthroplasty (UKA), patellofemoral arthroplasty (PFA), or total knee arthroplasty (TKA). All available literature published from 2000 to 2018 was reviewed to provide a comprehensive update regarding RTS incidence rates, time postoperatively RTS occurred, symptoms and limitations with sports participation, failure and revision rates, and rehabilitation criteria. Data from 21 studies after medial UKA showed an average RTS incidence rate of 78% (range, 53–90%), and data from 21 studies after TKA showed an average RTS incidence rate of 72% (range, 34–100%). There were too few studies of lateral UKA and PFA in which RTS information was provided to reach a conclusion. Nearly all studies reported return to low-impact activities such as walking for exercise, swimming, bicycling, hiking, bowling, and golf. None of the studies provided rehabilitation exercises and criteria used to determine when RTS was feasible. We provide our rehabilitation protocols for UKA, PFA, and TKA and criteria to begin recreational sport training for activities such as tennis and skiing.

There are many barriers that prevent or delay return to sports (RTS) after anterior cruciate ligament reconstruction. Some of the most common physical obstacles are residual knee pain, swelling, and/or instability. Research over the last two decades has demonstrated that psychological and psychosocial problems also play an important role in the inability of athletes to return to preinjury activity levels. Fear of reinjury or reinjury anxiety, poor perceived self-efficacy, low levels of internal locus of control, poor motivation, and emotional disturbances have all correlated with failure to RTS. Knowledge of these factors is crucial for those involved with the medical management of athletes in order to screen, detect, and initiate treatment and counseling.

The majority of patients who undergo anterior cruciate ligament (ACL) revision reconstruction do so in order to resume sports activities, and patients’ expectations appear to be nearly as high as those who undergo primary ACL reconstruction. Unfortunately, these patients frequently have associated problems from meniscectomy, articular cartilage damage, chronic neuromuscular deficiencies, swelling, and arthritic pain. The question of whether return to preinjury strenuous activity levels in ACL revision knees is advisable in light of the complexities involved requires analysis of existing investigations. We reviewed 20 modern clinical studies to determine return to sport (RTS) and subsequent graft failure/reinjury rates and whether symptoms were incurred during sports participation. The follow-up time periods were short to mid-term (range, 1–7.5 years), and return to preinjury sport activity levels varied widely, from 13% to 100%. Objective criteria to resume sports activities were provided only in four studies. Failure rates of ACL revision grafts ranged from 0% to 24%, and many failures were atraumatic in nature. Seven studies were conducted by survey only, and in these instances the graft failure rates may be higher than those reported. The effect of the graft selected for the revision procedure on RTS and failure rates could not be determined. Only two studies determined if patients were able to participate in sports without knee-related problems. The question of whether patients are able to participate in sports for many years after ACL revision reconstruction remains unanswered. We advise the return to low-impact activities after ACL revision in the majority of cases, especially in patients who have undergone meniscectomy or in whom arthritic damage or symptoms are present.

This chapter summarizes return to sport (RTS) and reinjury data after anterior cruciate ligament (ACL) reconstruction in 42,275 patients from 95 studies published from 2004 to 2018. Three major categories of subjects are presented: amateur athletes of all ages (40 studies, 29,711 athletes), children and adolescent athletes (31 studies, 10,661 athletes), and elite collegiate and professional athletes (23 studies, 1903 athletes). In addition, factors associated with RTS and reinjuries (to either knee) from both univariate and multivariate analyses when conducted by the investigations are described. Criteria for release to unrestricted sports activities are detailed and an update provided from our previously published systematic review. Recommendations are provided for each category of athlete, taking into consideration the potential deleterious effects of premature RTS and reinjuries, as well as need for future ACL revision reconstruction.

This chapter summarizes data in the current literature regarding return to sports (RTS) after patellofemoral realignment surgery from 52 studies encompassing 1892 patients. There were 1408 patients in 36 studies that underwent medial patellofemoral ligament (MPFL) reconstruction or repair and 484 patients in 16 studies that underwent a variety of patellar proximal and/or distal realignment procedures that did not involve MPFL reconstruction or repair (such as Fulkerson and Elmslie-Trillat). Following MPFL reconstruction, a mean of 70% of patients returned to preinjury sports activity levels, a mean of 83% returned to any sport, and the approximate mean postoperative Tegner score was 5.2 points. After other proximal/distal procedures, the mean values for return to preinjury sports (provided in only 5 studies) ranged from 22% to 97% and the mean postoperative Tegner score was 4.1 points. The mean time patients were usually allowed to RTS was provided in 28 studies and varied from 3 to 9 months postoperatively. Almost no objective criteria were provided to determine when patients could be safely released to either sports-specific training or unrestricted athletic activities. The failure rates were

This chapter reviews the scientific principles and concepts for anterior cruciate ligament reconstruction postoperative rehabilitation programs. The scientific concepts and basis for immediate knee motion and weight-bearing, as well as early restoration of muscle strength and neuromuscular function, are presented. Potential major complications are discussed, including infection, deep venous thrombosis, arthrofibrosis, complex regional pain syndrome, and patella infera, to enable early detection and treatment. The exercises and modalities used for programs are presented. Criteria are provided to advance the patient in a manner that is safe to the healing graft and responsive to the patient’s final activity level goals.

The decision of when to release an athlete to unrestricted sports activities after major knee surgery is based on many factors, including successful completion of advanced rehabilitation, psychological readiness, completion of advanced neuromuscular training programs appropriate for the desired sport, and a comprehensive examination by the physician. This chapter details the essential components of the physician’s examination, including the assessment of knee motion, gait, patellofemoral indices, meniscus retears, ligament function, and use of appropriate imaging studies. Guidelines for the use of knee arthrometer testing (KT-2000) and muscle strength assessment are provided. Facilitation of communication with the entire medical team involved in the patient’s care may be accomplished using the International Knee Documentation Committee’s objective knee evaluation form. Our comprehensive evaluation and criteria for return to unrestricted sports activities are summarized.

This chapter summarizes data in the current literature regarding return to sport (RTS) after meniscus surgery from 58 studies encompassing 2755 patients. There were 755 patients in 15 studies that underwent meniscectomy, 948 patients in 25 studies that had meniscus repair, and 1052 patients in 18 studies that underwent meniscus transplantation. Rates for return to preinjury sport, return to any type of sport, failures (meniscus repairs and transplants), and progression of knee osteoarthritis are provided. An analysis of the postoperative rehabilitation criteria for RTS described by each study is presented. Although high RTS rates were noted in a few meniscectomy studies in this chapter, these were offset by deterioration in radiographic knee osteoarthritis in 60–90% of patients followed >6 years postoperatively. A recommendation is made to preserve meniscus tissue and function through modern repair procedures whenever possible, especially in children and adolescent athletes. While sports are feasible after meniscus transplantation, the majority of studies recommend return to only low-impact or general athletic training due to pre-existing articular cartilage damage.

This chapter reviews common tests used to measure lower extremity muscle strength and dynamic balance stability. Advantages, disadvantages, and normative data are provided to assist the clinician in the selection and interpretation of test results. After major knee surgery, objective muscle strength and dynamic balance tests are used to advance patients through the initial phases of rehabilitation and before return to running and agility training, plyometric and advanced neuromuscular training, and final release to full sports activities. Although muscle strength is commonly evaluated in the clinic with a hand-held dynamometer using isometric resistance, isokinetic testing is preferred because it involves dynamic muscle performance. Correlations between muscle strength measured isokinetically and functional movements have been reported in multiple studies. Isometric testing of muscle strength on an isokinetic dynamometer is a valuable option for patients who have contraindications to isokinetic test protocols. We use this strength measurement early after surgery to protect healing ligament grafts or in cases of patellofemoral pain. If isokinetic or isometric equipment are not available, a 1-repetition single leg maximum leg press is recommended if weight room equipment, an experienced test administrator, and a sufficient amount of time to safely conduct the test are available. A variety of single-leg dynamic balance tests are described, all of which can be conducted in any clinical setting with minimal equipment.

Injury to the anterior cruciate ligament (ACL) can lead to significant dysfunction and instability in athletes. Over the last several decades, a vast body of research has been published on reconstruction techniques to restore knee stability and limit future injury to the meniscus and chondral surfaces of the knee. Overall, satisfactory patient outcomes can be achieved with a high percentage of patients returning to high levels of activity. Despite extensive research on the natural history of ACL injuries, reconstructive techniques, and the biology of healing, there are still many unanswered questions. There are many potential factors for ACL failure and resultant laxity postoperatively. Despite proper patient selection, graft choice, surgical technique, and postoperative rehabilitation, there are still other factors still not completely understood that play a role in a successful patient outcome. The biological phenomenon known as ligamentization and the maturation process that the ACL graft undergoes is complex, intricate, and still a matter of debate. The healing process of the grafted ACL and its ultimate role in restoring normal function of the knee is still not completely understood; however, we aim to summarize the most current evidence to help guide decision-making in eventual safe return to sports (RTS) and activities.

This chapter discusses the indications and contraindications for anterior cruciate ligament (ACL) reconstruction, graft options, preoperative planning, anatomic graft placement issues, and treatment of additional injuries that may occur to the menisci and other knee ligaments. Operative techniques are summarized for bone-patellar tendon-bone, semitendinosus-gracilis, and quadriceps tendon-bone autografts. Graft location required for an anatomic reconstruction is detailed. The results of our clinical studies on the outcome of ACL reconstruction are summarized. Indications and surgical techniques for repair of meniscus tears are provided, as well as the results of our clinical studies of meniscus repairs for tears extending into the central avascular region.

This chapter reviews commonly used scales that have been used to rate athletic activities for a variety of knee injuries and disorders. The instruments are analyzed according to their strengths and potential biases as well as their measured reliability, validity, and responsiveness properties.

This chapter reviews the running, agility, basic plyometric, and advanced Sportsmetrics neuromuscular training programs for anterior cruciate ligament reconstruction postoperative rehabilitation. The exercises are detailed, with the criteria provided to advance the patient through training in a manner that is safe and responsive to the patient’s final activity-level goals. Our comprehensive objective assessment of muscle strength, neuromuscular function, balance, range of knee motion, and ligament stability required for release to unrestricted athletics is provided.

This chapter presents a comprehensive rehabilitation program that should be performed before ACL reconstruction and documents data from multiple studies that demonstrate the advantages of formal preoperative therapy in terms of restoration of knee motion, muscle strength, and neuromuscular function. Major issues to treat and resolve before surgery are discussed, including hemarthrosis and knee joint effusion, pain, muscle weakness and inhibition, and abnormal gait mechanics.

This chapter reviews cost-effective tests to determine neuromuscular function and indicators of athletic performance regarding agility and aerobic capacity. Tests are recommended that depict neuromuscular function and abnormal mechanics during activities such as landing from a jump, cutting, or side-stepping. The most common field tests for assessing agility for a variety of sports are described, including the t-test, pro-agility test, Illinois agility test, and the 505 test. The multistage fitness test, commonly used to estimate maximal oxygen uptake, and the two Yo-Yo intermittent recovery tests, commonly used to evaluate an athlete’s ability to repeatedly perform intermittent exercise, are detailed. Reliability references are provided for each test, along with normative data of a wide variety of athletes sorted according to sport, gender, and age.

This chapter describes training techniques essential for return to soccer and basketball after major knee injury or surgery. Exercises and drills designed to improve dynamic balance, agility, speed, strength, and aerobic conditioning are illustrated and described in detail. Field tests are described that measure lower extremity power and dynamic balance, upper body strength and power, speed and agility, abdominal strength and endurance, and aerobic fitness. Reference material for training elite players is given, along with normative data regarding strength, power, speed, agility, and aerobic fitness. The authors’ programs, Sportsmetrics Soccer and Sportsmetrics Basketball, were found to be safe and effective in improving neuromuscular indices and athletic performance indicators in youth players and are recommended as end-stage rehabilitation after a knee injury or surgery before return to these activities.

Context:Blood flow–restricted training (BFRT) has been suggested to treat lower extremity muscle weakness. The efficacy of BFRT for muscle problems related to knee pathology is unclear.Objective:To determine whether BFRT (1) improves muscle strength and cross-sectional area (CSA) for chronic knee-related lower extremity atrophy and (2) prevents muscle atrophy after knee surgery.Data Sources:A systematic review of the literature from 1974 to 2017 was conducted using the PubMed and Cochrane databases.Study Selection:Controlled trials that used BFRT to treat chronic knee-related lower extremity muscle atrophy or to prevent muscle atrophy after knee surgery that measured the effects on quadriceps or hamstrings muscle strength or CSA were included.Study Design:Systematic review.Level of Evidence:Level 2.Data Extraction:Data were extracted as available from 9 studies (8 level 1, 1 level 2). Assessment of study quality was rated using the Physiotherapy Evidence Database or Methodological Index for Non-Randomized Studies instruments.Results:BFRT was used after anterior cruciate ligament reconstruction and routine knee arthroscopy and in patients with knee osteoarthritis or patellofemoral pain. There were a total of 165 patients and 170 controls. Vascular occlusion and exercise protocols varied; all studies except 1 incorporated exercises during occlusion, most of which focused on the quadriceps. Six of 7 studies that measured quadriceps strength reported statistically significant improvements after training. Few benefits in quadriceps CSA were reported. Hamstrings strength was only measured in 2 studies. There were no complications related to training.Conclusion:Published limited data show BFRT to be safe and potentially effective in improving quadriceps muscle strength in patients with weakness and atrophy related to knee pathology. The use of short-duration vascular occlusion and light-load resistance exercises appears safe after knee surgery or in arthritic knees. This treatment option requires further investigation to refine protocols related to cuff pressure and exercise dosage and duration.

Context: Total knee arthroplasty (TKA) is routinely performed in younger patients who desire to be active in fitness and recreational sports. The activities patients can participate in without symptoms and the level of aerobic fitness routinely maintained are important to investigate. Objective: To determine physical activity (PA) and recreational sports resumed after primary TKA, symptoms or limitations with these activities, and the effect of postoperative rehabilitation on achieving fitness and sports goals. Data Sources: A systematic review of the literature from 2005 through 2015 was conducted using the PubMed database. Study Selection: Original investigations that were conducted at least 1 year after primary TKA and reported the percentage of patients who returned to recreational activities or routinely participated in aerobic PA recommended by the American Heart Association (AHA) were included in this study. Study Design: Systematic review. Level of Evidence: Level 4. Data Extraction: Data were extracted as available from 19 eligible studies. Assessment of study quality was rated using the MINORS (Methodological Index for Non-Randomized Studies) instrument. Results: There were 5179 knees (mean age, 67.5 years) followed for a mean 4.8 years postoperatively. Marked variability was present between studies regarding the percentage of patients who resumed recreational activities (34%-100%), most of which were low impact. Only 2 studies used accelerometers to measure PA; these reported a low range (0%-16.5%) of patients who met AHA guidelines. Few studies determined whether symptoms or limitations were experienced during PA. None described rehabilitation exercises or factors that would influence patients’ ability to return to recreational or fitness activities. Conclusion: Little evidence is available regarding the effect of TKA on return to recreational and (objectively measured) aerobic fitness. The extent of symptoms or limitations during PA and the long-term effects of such problems remain unclear. Valid predictions cannot be made on factors that may affect return to recreational sports or other aerobic PA after TKA.

Background: Clinical outcomes and survivorship of meniscus transplants remain unclear, especially when magnetic resonance imaging (MRI) and weightbearing radiographic findings are included as endpoints. Many studies calculate survivorship based only on subsequent operative procedures. Purpose: We prospectively determined long-term survivorship and functional outcomes of 72 consecutive meniscus transplants. The effects of articular cartilage damage, concurrent osteochondral autograft transfer (20 knees), patient age, and tibiofemoral compartment were evaluated. Study Design: Case series; Level of evidence, 4. Methods: The long-term function and survival rates of 69 of 72 consecutive medial and lateral bone-meniscus-bone transplants (96% follow-up) were determined. Survival endpoints of reoperations, MRI failure (grade 3 signal intensity, extrusion >50% of meniscal width), meniscal tear on examination, and radiographic loss of joint space provided a worst-case outcome. Long-term functional analysis was performed in 58 transplants a mean of 11.9 ± 3.2 years postoperatively. The Cincinnati and International Knee Documentation Committee rating systems were used to evaluate outcomes. Results: For all transplants, the estimated probability of survival was 85% at 2 years, 77% at 5 years, 69% at 7 years, 45% at 10 years, and 19% at 15 years. There were significant improvements for pain, swelling, walking, stair climbing, and patient knee rating ( P < .05). Further surgery was performed in 37 cases. Knees that had concurrent osteochondral autograft transfer had significantly lower survival rates beginning at the seventh postoperative year; however, there was no significant difference in the long-term symptom, function, and patient perception scores between these knees and the rest of the cohort. The factors of articular cartilage damage (grade 2B/3 vs none), patient age (Conclusion: A survival analysis that includes reoperations, MRI, radiographs, and a comprehensive examination provides a worst-case but realistic analysis of transplant function. Many patients experienced a short- and long-term benefit of reduced symptoms and improved function. However, meniscus transplants undergo a deleterious remodeling process and eventually fail. Patients should be advised that the procedure is not curative in the long term, and additional surgery will likely be required.

Purpose To determine the effect of 2 extra-articular reconstructions on pivot-shift rotational stability and tibial internal rotation as a basis for clinical recommendations. Methods A robotic simulator tested 15 cadaver knees. Group 1 (anterior cruciate ligament [ACL] cut) underwent ACL bone-patellar tendon-bone reconstruction followed by sectioning the anterolateral structures and an extra-articular, manual-tension iliotibial band (ITB) tenodesis. Group 2 (ACL intact) tested the rotational stabilizing effect of a low-tension ITB tenodesis before and after sectioning the anterolateral ligament/ITB structures. Lateral and medial tibiofemoral compartment translations and internal-external tibial rotations were measured under Lachman, 5N·m tibial rotation, and 2 pivot-shift simulations using 4-degree-of-freedom loading. Statistical equivalence was defined within 2 mm tibiofemoral compartment translation and 2° tibial rotation at P Results The bone-patellar tendon-bone ACL reconstruction (group 1) restored pivot-shift lateral compartment translation within 0.7 mm (95% confidence interval [CI], -0.6 to 1.9; P = .70) of normal. The internal rotation limit was not affected by ACL sectioning or reconstruction. After anterolateral ligament/ITB sectioning there was no change in pivot-shift lateral compartment translation, however internal rotation increased 2.9° (95% CI, 0.6-5.2; P = .99) at 90° flexion. The manual-tension ITB tenodesis (fixated 13-22 N tension) decreased pivot-shift lateral compartment translation 4.8 mm (95% CI, 1.4-8.1; P = .99) and internal rotation by 21.9° (95% CI, 13.2-30.6; P = .99) at 90° flexion. The ACL forces decreased 45.8% in the pivot-shift test. In group 2 knees, with the ACL intact, the anterolateral ligament/ITB sectioning had no effect on pivot-shift translations; however, the internal rotation limit increased by 4.3° (95% CI, 1.9-6.8; P = .99) at 60° flexion. The low-tension ITB tenodesis (fixated 8.9 N tension) had no effect on pivot-shift translations and corrected internal tibial rotation with a mild overconstraint of 4.2° (95% CI, 1.9-6.8; P = .99) at 60° flexion. Conclusions A low-tension ITB tenodesis, fixated at neutral tibial rotation to avoid constraining internal tibial rotation, has no effect in limiting abnormal pivot-shift subluxations. Clinical Relevance A low-tension ITB tenodesis has limited clinical utilization as the pivot-shift subluxations are not affected, assuming appropriate tensioning to not overconstrain internal tibial rotation.