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BACKGROUND Infants with more severe brachial plexus birth injury (BPBI) benefit from primary nerve surgery to improve function. The timing of the surgery, however, is controversial. The Treatment and Outcomes of Brachial Plexus Injury (TOBI) study is a multicenter prospective study with the primary aim of determining the optimal timing of this surgical intervention. This study compared outcomes evaluated 18 to 36 months after "early" microsurgery (at 6 months of age). METHODS Of 216 patients who had undergone microsurgery, 118 were eligible for inclusion because they had had a nerve graft and/or transfer followed by at least 1 physical examination during the 18 to 36-month interval after the microsurgery but before any secondary surgery. Patients were grouped according to whether the surgery had been performed before or after 6 months of age. Postoperative outcomes were measured using the total Active Movement Scale (AMS) score as well as the change in the AMS score. To address hand reinnervation, we calculated a hand function subscore from the AMS hand items and repeated the analysis only for the subjects with a Narakas grade of 3 or 4. Our hypothesis was that microsurgery done before 6 months of age would lead to better clinical outcomes than microsurgery performed after 6 months of age. RESULTS Eighty subjects (68%) had early surgery (at a mean age of 4.2 months), and 38 (32%) had late surgery (at a mean age of 10.7 months and a maximum age of 22.0 months). Infants who underwent early surgery presented earlier in life, had more severe injuries at baseline, and had a significantly lower postoperative AMS scores in the unadjusted analysis. However, when we controlled for the severity of the injury, the difference in the AMS scores between the early and late surgery groups was not significant. Similarly, when we restricted our multivariable analysis to patients with a Narakas grade-3 or 4 injury, there was no significant difference in the postoperative AMS hand subscore between the early and late groups. CONCLUSIONS This study suggests that surgery earlier in infancy (at a mean age of 4.2 months) does not lead to better postoperative outcomes of BPBI nerve surgery than when the surgery is performed later in infancy (mean age of 10.7 months). LEVEL OF EVIDENCE Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

CASE We present the case of an infant with an amputation from amniotic band syndrome and no other complications. During the seventh week of life, the infant developed severe pain in the affected limb that was ultimately found to be indicative of osteomyelitis. CONCLUSION The infant displayed minimal systemic response, and cultures that grew methicillin-sensitive Staphylococcus aureus were needed to confirm the diagnosis. Surgical debridement, stump revision, and oral antibiotic therapy provided definitive treatment for our patient. The reader is encouraged to consider the possibility of osteomyelitis in similar circumstances.

Thyroid hormone has been implicated in the normal growth and development of articular cartilage; however, its effect on a disease state, such as hypothyroidism, is unknown. The purpose of this investigation was to compare normal articular cartilage from proximal femurs of immature miniature swine to proximal femurs from hypothyroid-induced immature miniature swine.Two 11-week-old male Sinclair miniature swine were made hypothyroid by administration of 6-propyl-2-thiouracil (PTU) in their drinking water; two control animals did not receive PTU. At 25 weeks of age, the animals were euthanized and their proximal femurs were fixed and decalcified. Samples were sectioned and analyzed by histology to define extracellular matrix (ECM) structure, immunohistochemistry (IHC) to identify types II and X collagen, and histomorphometry to assess articular cartilage mean total and localized height and cell density. Statistics included nested mixed-effects ANOVA with p ≤ 0.05 considered statistically significant.Compared to controls, hypothyroid articular cartilage demonstrated statistically significant quantitative differences in mean tissue height, mean cell density and type II collagen localized zone height. Qualitative differences in ECM proteoglycans and overall collagen types were also found. Type X collagen was not detected in either hypothyroid or control articular cartilage specimens.Significant changes in articular cartilage structure in hypothyroid compared to control immature miniature swine suggest that thyroid hormone is critical in the growth and development of articular cartilage.Understanding articular cartilage development in immature animal models may provide insight into healing or repair of degenerative human articular cartilage.

Brachial plexus birth palsy (BPBP) is a neurologic injury that can result in mild to full paralysis of the affected upper extremity. In severe cases, nerve surgery is often performed before age 1 year. Several studies report gains in elbow flexion with onabotulinum toxin type A (OBTT-A) injections to the triceps; however, its use in infants is not widely reported. The purpose of this study is to present our experience using these injections before 6 months of age to therapeutically unmask elbow flexion and diagnostically guide surgical decision making. This is a retrospective observational cohort study. The cohort included infants with BPBP who received OBTT-A injection to the triceps before age 6 months. Indications for the injections include trace elbow flexion and palpable co-contraction of the biceps and triceps. Elbow flexion was evaluated using the Toronto Test score. Therapeutic success was defined as an increase in post-injection scores. These scores were then used diagnostically as an indication for surgery if the infant did not achieve full elbow flexion by 8 months. A treatment algorithm for OBTT-A triceps injection was developed based on all treatment options offered to infants with elbow flexion deficits seen in the clinic. Of the 12 infants that received OBTT-A triceps injections, 10 (83%) had improved Toronto test elbow flexion scores post-injection. Gains in elbow flexion once attained were maintained. Of the 9 OBTT-A infants with at least 2 years follow-up, 4 achieved full elbow flexion without surgery; the remainder after surgery. No complications with OBTT-A injections were noted and patients were followed on average 6 years. The average age at time of injection was 4 months (range: 2–5 months). Compared to other treatments given, OBTT-A infants tended to present with more elbow flexion than the 4 infants requiring immediate surgical intervention and less elbow flexion than the 16 infants treated conservatively. OBTT-A injection to the triceps in infants with BPBP before 6 months of age therapeutically improved elbow flexion and diagnostically guided surgical decisions when full elbow flexion was not achieved by 8 months of age with no known complications.

INTRODUCTION Pediatric supracondylar humerus fractures are associated with a high incidence of nerve injury. Therefore, it is imperative that documentation be complete and accurate. This investigation compares orthopaedic resident history and physical (H&P) documentation of pediatric supracondylar fractures for completeness and accuracy with and without the use of an electronic medical record template. METHODS The electronic medical record H&P documentation of 119 supracondylar humerus fractures surgically treated at a single pediatric institution was retrospectively reviewed. Templated and nontemplated groups were compared for documentation completeness and accuracy. Definitive diagnosis of a nerve palsy was made by a supervising orthopaedic attending surgeon. RESULTS Forty-two cases had a templated H&P and 77 did not. The H&P documentation in the templated group was markedly more complete than that in the nontemplated group. However, the accuracy of the H&P documentation to identify nerve palsy was not statistically different between the two groups. Overall, the voluntary use of the orthopaedic template declined over time. CONCLUSION Resident use of an orthopaedic template for documenting the H&P of pediatric supracondylar humerus fractures compared with nontemplated notes resulted in more complete documentation but only comparable accuracy. LEVEL OF EVIDENCE III.

Background: The etiology for recurrent patellar dislocations in children with patellofemoral instability (PFI) is not always apparent. Radiographic and other imaging measures help guide the clinician. However, the imaging parameters for pathologic pediatric PFI and the significance of these measures based on severity are not clearly defined. This study compares common imaging measures for PFI in a non-pathologic and known patellar dislocation pediatric population and determines the likelihood of symptoms based on the severity of each individual measure. Methods: An IRB-approved retrospective review of knee MRIs and radiographs at a single pediatric institution identified 108 limbs (102 patients) meeting inclusion criteria. Sixty-nine limbs had no known patellar pathology (control group) and 39 had surgery for recurrent patellar dislocations (surgical group). MRI measures included tibial tuberosity-trochlear groove distance (TT-TG), tibial tuberosity-posterior cruciate ligament distance (TT-PCL), and lateral trochlear inclination (LTI). Radiographic measures included the Caton-Deschamps Index (CDI) and Insall-Salvati Index (ISI). These measures are representative of PFI risk factors, specifically patellar tendon malalignment, trochlear dysplasia, and patella alta. Binomial logistic regression was used to relate the anatomical parameters to the probability of PFI. Results: The surgical and control groups were similar in terms of age, height and weight. The logistic regression analysis indicated that the TT-TG (p=0.001) and LTI (pConclusion/Significance: Comparing pediatric patients with recurrent patellar dislocations to controls, logistic regression analysis suggests the likelihood of PFI correlates with the severity of specific radiographic measures, specifically those representing the degree of patellar tendon alignment (TT-TG) and trochlear dysplasia (LTI). Knowing this correlation can help guide the treatment of PFI in pediatric patients by providing physicians and families with a continuum on which to base their decisions.

Background: Microarray technology has been used to analyze gene expression in patients with and without slipped capital femoral epiphysis (SCFE). Methods: Proximal femoral physis core biopsies from two patients with SCFE were compared with two control specimens from age-matched patients without SCFE. Extracted RNA from frozen ground samples was subjected to microarray analysis with data tests for statistical significance between SCFE and control tissues. Results: Compared to controls, SCFE samples demonstrated significant up-regulation in gene expression pathways involving physiological defense and inflammatory responses and significant down-regulation in the regulation of cellular physiologic processes, cellular metabolic pathways, and skeletal development pathways including expression of aggrecan and type II collagen, genes affecting physeal structure and integrity. Conclusions: Up-regulation of inflammatory and immune response pathways in SCFE compared to controls relates to physeal mechanical displacement in SCFE. Globalized down-regulation of several other pathways suggests growth plate weakening. These novel microarray findings further define SCFE etiology.

Current surgical options for treating genu varum in achondroplasia include tibial and fibular osteotomy and growth modulation using plates and screws. However, a single surgeon consistently treated genu varum using a planned fibular nonunion (PFN). The purpose of this study is to describe his surgical technique and report radiographic and clinical outcomes for the cohort studied.This is an observational retrospective review. The cohort studied included patients with achondroplasia who had PFN surgery for the treatment of genu varum at a young age (

Effective multimodal analgesia and sedation reduce the postoperative morbidity and mortality associated with newborn bladder exstrophy repair. Epidural analgesia is safe and effective for major surgery in neonates and infants, reducing the need for muscle relaxants, opioids, and ventilator support postoperatively. The risk of epidural catheter colonization typically dictates removal after 3 to 5 days. Tunneling the catheter subcutaneously reduces the risk of colonization, providing prolonged analgesia for patients requiring an extended immobilization to prevent compromise of the repair. In this report, we describe the postoperative analgesic management of an infant undergoing bladder exstrophy repair using a directly placed tunneled epidural catheter with ropivacaine 0.1% infusion. Because of the prolonged infusion, we also monitored plasma ropivacaine levels to preclude systemic toxicity from local anesthetic overdose.

Purpose In situ fixation for mild to moderate slipped capital femoral epiphysis (SCFE) remains an acceptable treatment methodology in most centers. Satisfactory fixation results have been reported with the procedure using either the fracture table or radiolucent table, both of which allow the hip to be imaged during the procedure. The position of the pin within the center of the femoral head is important to secure adequate fixation of the capital femoral epiphysis and prevent further slippage with minimal risk for articular penetration and avascular necrosis (AVN) or chondrolysis. Methods We describe a pre-operative planning technique to determine the pin-entry point for percutaneous pinning of SCFE on a radiolucent operating table. A retrospective review of patients who underwent in situ screw fixation with the usage of a cannulated screw on a radiolucent table or fracture table over a 6-year period was conducted. Results The pin-entry point with this technique was reliable in 92% of procedures and comparable in both accuracy and complications to in situ screw fixation on a fracture table. In situ screw fixation on a regular radiolucent table was straightforward and required significantly less surgical time than on the fracture table ( P = 0.01). It was also more efficient during a bilateral procedure, as it required only a single preparation and draping of the patient. Conclusion This pre-operative planning technique for deciding the starting point on the proximal femur is helpful in executing an accurate in situ screw fixation of hips with SCFE.

The purpose of this study was to compare the biomechanical stability of triple innominate osteotomies fixed with either bioabsorbable or stainless steel screws. Triple innominate osteotomies were performed on composite hemipelves and fixed with either three 4.5-mm bioabsorbable screws or three stainless steel 4.5-mm screws. Two screws were placed from the iliac wing into the acetabular fragment, and 1 screw was placed from below the acetabular fragment into the iliac wing. Eight specimens for each screw type were biomechanically tested in an anatomical position (replicating weight bearing) and in a flexed and abducted position (replicating spica cast positioning). Specimens were cyclically loaded between 10 and 450 N to simulate the hip contact force in this population. Lower screws were then removed, and specimens were tested under identical conditions. Fragment displacement (mm) and construct stiffness (N/mm) were compared with a 2-way analysis of variance (P < 0.05). There were no significant differences between materials for fragment displacement or construct stiffness. Anatomical position showed significantly less displacement than spica position for both materials. Initial displacement in the spica position was significantly less during lower loads for stainless steel fixation. Bioabsorbable screws demonstrate comparable biomechanical stability to stainless steel screws in anatomical and spica positions at physiological loads. Flexion and abduction of the femur adversely affect the stability of the construct for both materials. Bioabsorbable screws behave similarly to steel screws when stabilizing triple innominate osteotomies and would have the advantage of not requiring a second surgery for screw removal. Confirmation of biocompatibility should be completed before widespread clinical application.

Previous studies documented the use of fibular allograft in the treatment of slipped capital femoral epiphysis (SCFE) with bone graft epiphysiodesis (BGE). This study describes the results of using a 10-mm diameter premilled fibular allograft packed with demineralized bone matrix placed across the physis in an open surgical approach under image intensification. A review identified 45 cases of BGE using fibular allograft and demineralized bone matrix in 34 patients with a diagnosis of SCFE performed by a single surgeon during an 8-year period. Thirty-four cases (25 patients) had at least 1 year of follow-up and were included in the study. Medical records were reviewed for complications, subsequent surgeries, and time to physeal closure. Of the 34 cases included, there were no cases of acute chondrolysis. Complications included 1 case of bone graft extrusion that required surgical replacement and 1 re-slip requiring surgical stabilization. Five cases of avascular necrosis (AVN) were encountered (1 unstable slip with total head AVN, and 4 stable slips with 3 total head and 1 partial head AVN). In 1 patient, small loose bony fragments were noted on postoperative radiographs that appeared outside of the articular surface of the hip and were asymptomatic. Two patients encountered wound healing issues that resolved with appropriate wound care. In light of the occurrence of AVN in stable cases, BGE with autogenous corticocancellous graft is preferable to BGE with autologous fibular graft for the treatment of SCFE. [ Orthopedics. 2016; 39(3):e519–e525.]

Retrospective case series.To compare radiographic and clinical outcomes in posterior spine fusions with pedicle screw instrumentation of varying screw densities in the treatment of adolescent idiopathic scoliosis (AIS).Posterior spinal fusion with pedicle screw instrumentation is the mainstay of surgical treatment for AIS. The most commonly used construct consists of screws placed at every level on the concave side of the deformity and nearly every level on the convex side. However, some surgeons have begun using constructs with fewer pedicle screws. The literature comparing outcomes of these differing pedicle screw constructs is limited.Fifty-two consecutive cases of posterior spinal fusions for AIS performed by four surgeons were reviewed. High screw density constructs were used in 26 cases and limited screw density constructs in 26 cases. Construct characteristics and radiographic measurements were compared preoperatively and at last follow-up. Operative time and estimated costs were also evaluated. Student t tests were used to compare the groups with p.05 considered significant.There was no significant difference in magnitude of correction for the high versus limited screw density group initially (38.5° vs. 34.9°, p = .093) or at final follow-up (36.9° vs. 32.2°, p = .054). Sagittal alignment, coronal balance, and translation of the major apical vertebra were comparable and stable in both groups. The high versus limited screw density group utilized significantly more pedicle screws (16.8 vs. 11.6 screws, p.0001), had longer operative times (309 vs. 267 minutes, p = .007), and had additional estimated direct costs of $5,800.Excellent curve correction, stability, and balance can be achieved using fewer screws than commonly used in posterior pedicle screw fusions for AIS. Operative time is reduced, and risk and cost are decreased with the use of limited screw density constructs.III.

Delayed unions and nonunions of diaphyseal pediatric forearm fractures are exceedingly uncommon. In the past they generally have been reported in conjunction with open fracture or initial operative management of these fractures. The authors report six cases that occurred in low-energy, closed fractures initially managed with casting. The cases all occurred in teenage patients from age 13 to 16, and all cases involved the ulna. The mid-diaphysis was the most common location, and this may represent a watershed zone of perfusion with a relatively poor intraosseous blood supply. All of these patients were managed with compression plating with or without bone grafting. Three of these patients had rapid healing in an average of 2 months, while one had an inadequate radiographic record and another was lost to follow-up. The other patient had a more prolonged course to healing after surgery.

A "millennium" update of all cases of slipped capital femoral epiphysis treated by bone graft epiphysiodesis between 1950 and 2000 was conducted. All cases were followed for at least 1 year to evaluate the occurrence of re-slippage, avascular necrosis (AVN), chondrolysis, or complications secondary to the surgical approach. This study adds 109 patients and 133 hips to the initial report for a total of 268 patients and 318 hips. The patients include 43 patients with 45 acute slips and 225 patients with 273 chronic slips. The results include three cases of AVN, six cases of re-slippage, one case of chondrolysis, and no surgical approach complications in the acute group. In the chronic group, there were 4 cases of AVN, 17 cases of re-slippage, 4 cases of deep wound infection, and no cases of chondrolysis. The authors suggest that bone graft epiphysiodesis is a reasonable alternative in the treatment of slipped capital femoral epiphysis.

BACKGROUND: Jefferson (C1) fractures are rare cervical spine injuries that usually do not result in cranial nerve (CN) impairment. However, case reports of Collet-Sicard syndrome (impairment of CNs IX-XII) and impairment of CNs IX, X, and XII have been reported. All reported cases involved adult patients in high-impact collisions, such as motor vehicle accidents or falls. To our knowledge, a Jefferson fracture with selective CN impairment due to a low-energy, sports-related injury in a pediatric patient has not been reported. METHODS: Chart and radiographic data for a single case were reviewed and reported in a retrospective study approved by the Institutional Review Board of the participating hospital. RESULTS: A 16-year-old male was diagnosed with a Jefferson fracture after a head-to-chest football collision. On computed tomography, the distance between the atlas transverse process and styloid process of the skull was 5 mm right and 10 mm left. Before halo fixation, the patient had vague complaints of dysphagia. These complaints worsened which led to the diagnosis of CN IX and X impairment and placement of a feeding tube. The fracture healed uneventfully, the dysphagia symptoms resolved, and the halo fixation and feeding tube were removed. The patient returned to all activities, but was instructed to avoid participation in contact sports. CONCLUSIONS: This was the first report of selective CN impairment in a pediatric patient with a Jefferson fracture resulting from a low-impact sports-related injury. Careful monitoring of the patient complaints led to appropriate treatment. Further studies into the spatial relationship between the transverse process of the atlas in relation to the styloid process of the skull may be warranted. LEVEL OF EVIDENCE: Level V, case report. Language: en

BACKGROUND: Slipped capital femoral epiphysis (SCFE) is usually treated with percutaneous in situ screw fixation to prevent further progression of deformity. The purpose of this investigation is to compare computer navigation (CN) techniques with traditional fluoroscopic (fluoro) techniques for in situ fixation of SCFE. METHODS: This study was an IRB-approved prospective study of 39 hip pinnings in 33 children. CN techniques were used in 22 cases and fluoro in 17. The CN and fluoro groups were statistically similar in terms of grade and acuity of the slip. Children were assigned to the groups based on the intraoperative imaging technique used by the attending on call, with 3 surgeons in each group taking equal amounts of call. The "approach-withdraw" technique was used in all cases. Postoperative limited-cut, reduced-dose computed tomography (CT) scans were obtained to evaluate screw placement. This included blinded analysis for screw penetration of the joint, screw tip-to-apex distance, the distance the screw passed to the center of the physis, and attainment of center-center position. The number of pin passes, intraoperative radiation exposure, and operating room (OR) time were also analyzed. Statistics used included ANOVA, the χ and median tests. RESULTS: Compared with the fluoro group, CN resulted in more accurate screw placement. There was 1 case of joint penetration in the fluoro group not appreciated intraoperatively but detected on postoperative CT. CN also resulted in statistically significant (P < 0.05) reduced screw tip-to-apex distance and distance to the center of the physis. There was no statistically significant difference between the 2 groups in attainment of the center-center position, number of pin passes, or intraoperative radiation exposure. OR time averaged 19 minutes longer in the CN group. There was no case of avascular necrosis or chondrolysis in either of the groups. CONCLUSIONS: Compared with traditional fluoro techniques, CN in situ fixation of SCFE results in more accurate screw placement, comparable number of pin passes and intraoperative radiation exposure, and increased OR time. The cost-benefit ratio of this technology requires careful consideration at each individual institution. LEVEL OF EVIDENCE: II.

Scaphoid fractures are often missed in children because of their rarity and difficulty with radiographic diagnosis. Children are often treated for clinically suspected scaphoid fractures although there is no radiographic evidence for fracture on initial evaluation. The 2-fold purpose of this study is (1) to determine how many clinically suspected pediatric scaphoid fractures later became radiographically evident fractures and (2) to identify physical examination findings that suggest a scaphoid fracture when present at initial evaluation.We performed separate retrospective and longitudinal reviews of children younger than 16 years referred to orthopaedics with traumatic wrist pain from January 1995 to April 2002. A total of 104 cases with high clinical suspicion but no radiographic evidence of scaphoid fracture on initial examination were included. Patients were followed until discharge to determine if they later demonstrated a confirmed fracture. In the longitudinal arm, 7 specific examination findings were recorded. Simple and multiple logistic regressions were used to analyze the data.Thirty-one (30%) of the 104 wrists with no initial radiographic evidence of fracture had a radiographically evident scaphoid fracture at follow-up. In the longitudinal arm (n = 41), the following 3 findings were statistically significant predictors of scaphoid fracture: volar tenderness over the scaphoid (P = 0.010), pain with radial deviation (P = 0.001), and pain with active wrist range of motion (P = 0.015). Presence of any of these findings was associated with a higher likelihood of scaphoid fracture.A high percentage (30%) of clinically suspected scaphoid fractures in children became radiographically evident fractures at follow-up. Volar scaphoid tenderness, radial deviation pain, and pain with active wrist range of motion can be used as signs to increase suspicion for eventual fracture. We recommend that all clinically suspected pediatric scaphoid fractures be immobilized with repeat radiographs and a clinical examination at 2 weeks.II.

Ultrastructural studies of slipped capital femoral epiphysis (SCFE) growth plates have shown diminished cellularity and marked distortion of the architecture in the proliferative and hypertrophic zones. Chondrocyte degeneration and death were noted at all levels of the hypertrophic and proliferative zones, suggesting an accelerated disturbance in the life-to-death cycle of the chondrocytes. The current study examines the mechanism responsible for the diminished cell number and whether increased programmed cell death (apoptosis) or necrosis was operative. Proximal femoral growth plates from patients with SCFE (three patients) were prepared and sectioned for histochemistry, in situ detection of apoptosis, and immunohistochemistry. The results showed that the diminished cell number is due to an abnormal frequency and distribution of chondrocytes undergoing apoptosis. Although it is unclear whether the increased apoptosis is occurring early or late in the disease, it is highly likely that it is directly linked to pathogenesis.

Background: The effect of compression on the physis is generally defined by the Hueter-Volkmann principle, in which decreased linear growth of the physis results from increased compression. This investigation examined whether mechanically induced compression of rabbit physes causes changes in gene expression, cells, and extracellular components that promote physeal resilience and strength (type-II collagen and aggrecan) and cartilage hypertrophy (type-X collagen and matrix metalloprotease-13). Methods: Static compressive loads (10 N or 30 N) were applied for two or six weeks across one hind limb proximal tibial physis of thirteen-week-old female New Zealand White rabbits (n = 18). The contralateral hind limb in all rabbits underwent sham surgery with no load to serve as an internal control. Harvested physes were divided into portions for histological, immunohistochemical, and quantitative reverse transcription-polymerase chain reaction analysis. Gene expression was statistically analyzed by means of comparisons between loaded samples and unloaded shams with use of analysis of variance and a Tukey post hoc test. Results: Compared with unloaded shams, physes loaded at 10 N or 30 N for two weeks and at 10 N for six weeks showed histological changes in cells and matrices. Physes loaded at 30 N for six weeks were decreased in thickness and had structurally disorganized chondrocyte columns, a decreased extracellular matrix, and less intense type-II and X collagen immunohistochemical staining. Quantitative reverse transcription-polymerase chain reaction analysis of loaded samples compared with unloaded shams yielded a significantly (p ≤ 0.05) decreased gene expression of aggrecan and type-II and X collagen and no significant (p > 0.05) changes in the matrix metalloprotease-13 gene expression with increasing load. Conclusions: Compressed rabbit physes generate biochemical changes in collagens, proteoglycan, and cellular and tissue matrix architecture. Changes potentially weaken overall physeal strength, consistent with the Hueter-Volkmann principle, and lend understanding of the causes of pathological conditions of the physis. Clinical Relevance: Compressive forces across rabbit tibial physes cause changes in cartilage molecular biology, biochemistry, and structure, which may provide insight into disorders of the open physis in humans.