Femoroacetabular Impingement Measurements Obtained From Two-Dimensional Radiographs Versus Three-Dimensional-Reconstructed Computed Tomography Images Result in Different Values.

Purpose: To compare the reliability and accuracy of radiographic measurements obtained from 2-dimensional (2D) radiographs and 3-dimensional (3D)-reconstructed computed tomography (CT) images in the assessment of femoroacetabular impingement syndrome (FAIS). Methods: Consecutive patients with FAIS from January 2018 to December 2020 were identified and included in this study. Two fellowship-trained surgeons and 2 fellows performed blinded radiographic measurements. Lateral center-edge angle (LCEA) and Tönnis angles were measured on anteroposterior pelvic radiographs, and alpha angles were measured on frog lateral radiographs. Reliability coefficients for individual measurement accuracy were performed using the Cronbach alpha and intra- and inter-rater intraclass correlation coefficients (ICCs). Composite measurements for LCEA, Tönnis angle, and alpha angle were compared with the corresponding 3D value using paired sample t-tests. Results: Fifty-three patients with FAIS with standardized 2D radiographic and 3D-reconstructed CT imaging were included. All reliability metrics met thresholds for internal reliability. Inter-rater ICCs for LCEA, Tönnis angle, and alpha angle were (0.928, 0.888, 0.857, all P < .001). When we compared 2D radiographic measurements with 3D-reconstructed CT values, there was a significant difference in the LCEA for 2 authors: surgeon 1 (mean [M] = -9.14, standard deviation [SD] = 5.7); t(52) = -11.6, P < .001, and surgeon 2 (M = -5.9°, SD = 4.7); t(52) = -9.2, P < .001. Significant differences were seen for Tönnis angle for 2 authors: fellow 2 (M = 3.9°, SD = 5.6); t(52) = 5.1, P < .001, and surgeon 2 (M = -2.6°, SD = 4.1); t(52) = -4.6, P < .001. Alpha angle measurements compared to the 3D-reconstructed alpha angle at 2 o'clock was significantly different for 3 authors: fellow 1 (M = 11.9°, SD = 16.2); t(52) = 5.3, P < .001; fellow 2 (M = 10.4°, SD = 18.6); t(52) = 4.1, P = .002; and surgeon 2 (M = -6.5°, SD = 16.2); t(52) = -2.9, P = .005. Positive mean values indicate 2D radiographic measurements overestimated 3D reconstruction values and negative mean values indicate underestimation. Conclusions: The use of 2D radiographs alone for preoperative planning of FAIS may lead to inaccuracies in radiographic measurements. Level of Evidence: Level, III retrospective cohort study.

Monitoring Postoperative Opioid Use Following Simple Arthroscopic Meniscectomy: A Performance-Improvement Strategy for Prescribing Recommendations and Community Safety.

BACKGROUND: Orthopaedic surgeons are confronted with a difficult dilemma: managing acute pain postoperatively and balancing the risk of prescription opioid use. To our knowledge, a prospective performance-improvement project providing opioid-prescription recommendations based on the actual amounts of usual and customary medication consumed following simple knee meniscectomy has not been described. METHODS: One hundred and two patients undergoing arthroscopic knee meniscectomy prospectively recorded postoperative pain medications in a pain journal. Arthroscopic procedures were performed at 2 centers by 9 fellowship-trained senior surgeons. Various usual and customary prescribing protocols were observed, and the amount of medication consumed was recorded. Prescription and over-the-counter pain medication, quantity, frequency, and visual analog scale (VAS) pain scores were collected. RESULTS: One hundred and two patients filled a prescription opioid medication and were included in the study. A total of 3,765 pills were prescribed, and a total of 573.5 were consumed. For the 102 patients who filled a prescription, the average time consuming opioid medication was 2 ± 2 days (range, 0 to 13 days) postoperatively. No cases of persistent use were recorded. Of the 102 patients who filled a prescription, 29.4% did not take any prescription opioids postoperatively. A total of 3,191.5 pills (or 22,183.75 morphine milligram equivalents [MME]) were unused and were potentially available to the community. CONCLUSIONS: Following simple knee arthroscopy, the amount of prescribed opioid medication exceeds the need for postoperative pain management. In general, 68% of patients require a maximum of 13 pills postoperatively for 6 days. Surgeons should adjust prescribing standards accordingly to limit the amount of prescription opioids available to the community. Furthermore, a comprehensive response to include increased patient screening and monitoring as well as opioid use and disposal education is recommended.

Salvage of contaminated osteochondral allografts: the effects of chlorhexidine on human articular chondrocyte viability.

BACKGROUND: Because chondrocyte viability is imperative for successful osteochondral allograft transplantation, sterilization techniques must provide antimicrobial effects with minimal cartilage toxicity. Chlorhexidine gluconate (CHG) is an effective disinfectant; however, its use with human articular cartilage requires further investigation. PURPOSE: To determine the maximal chlorhexidine concentration that does not affect chondrocyte viability in allografts and to determine whether this concentration effectively sterilizes contaminated osteoarticular grafts. STUDY DESIGN: Controlled laboratory study. METHODS: Osteochondral plugs were subjected to pulse lavage with 1-L solutions of 0.002%, 0.01%, 0.05%, and 0.25% CHG and cultured for 0, 1, 2, and 7 days in media of 10% fetal bovine serum and antibiotics. Chondrocyte viability was determined via LIVE/DEAD Viability Assay. Plugs were contaminated with Staphylococcus aureus and randomized to 4 treatment groups. One group was not contaminated; the 3 others were contaminated and received no treatment, saline pulse lavage, or saline pulse lavage with 0.002% CHG. Serial dilutions were plated and colony-forming units assessed. RESULTS: The control group and the 0.002% CHG group showed similar cell viability, ranging from 67% ± 4% to 81% ± 22% (mean ± SD) at all time points. In the 0.01% CHG group, cell viability was reduced in comparison with control by 2-fold at day 2 and remained until day 7 (P < .01). The 0.05% and 0.25% CHG groups showed a 2-fold reduction in cell viability at day 1 (P < .01). At day 7, cell viability was reduced to 15% ± 18% (4-fold decrease) for the 0.05% CHG group and 10% ± 19% (6-fold decrease) for the 0.25% CHG group (P < .01). Contaminated grafts treated with 0.002% CHG demonstrated no colony-forming units. CONCLUSION: Pulse lavage with 0.002% CHG does not cause significant cell death within 7 days after exposure, while CHG at concentrations >0.002% significantly decreases chondrocyte viability within 1 to 2 days after exposure and should therefore not be used for disinfection of osteochondral allograft. Pulse lavage does not affect chondrocyte viability but cannot be used in isolation to sterilize contaminated fragments. Overall, 0.002% CHG was shown to effectively decontaminate osteoarticular fragments. CLINICAL RELEVANCE: This study offers a scientific protocol for sterilizing osteochondral fragments that does not adversely affect cartilage viability.

Retrospective analysis of arthroscopic superior labrum anterior to posterior repair: prognostic factors associated with failure.

Background. The purpose of this study was to report on any prognostic factors that had a significant effect on clinical outcomes following arthroscopic Type II SLAP repairs. Methods. Consecutive patients who underwent arthroscopic Type II SLAP repair were retrospectively identified and invited to return for follow-up examination and questionnaire. Statistical analysis was performed to determine associations between potential prognostic factors and failure of SLAP repair as defined by ASES of less than 50 and/or revision surgery. Results. Sixty-two patients with an average age of 36 ± 13 years met the study criteria with a mean followup of 3.3 years. There were statistically significant improvements in mean ASES score, forward elevation, and external rotation among patients. Significant associations were identified between ASES score less than 50 and age greater than 40 years; alcohol/tobacco use; coexisting diabetes; pain in the bicipital groove on examination; positive O'Brien's, Speed's, and/or Yergason's tests; and high levels of lifting required at work. There was a significant improvement in ASES at final followup. Conclusions. Patients younger than 20 and overhead throwers had significant associations with cases requiring revision surgery. The results from this study may be used to assist in patient selection for SLAP surgery.

Articular and meniscal pathology associated with primary anterior cruciate ligament reconstruction.

BACKGROUND: The abnormal kinematics, contact pressures, and repeated episodes of instability observed in chronic anterior cruciate ligament (ACL) deficiency suggest that these patients may be predisposed to early degenerative changes and associated pathologies such as meniscal tears and chondral injury. Injury to the cartilage and associated structures at the time of ACL rupture, in combination with the inflammatory mediators released at the time of injury, may create irreversible damage to the knee despite restoration of normal knee kinematics with an ACL reconstruction. HYPOTHESIS: Patients undergoing acute ACL reconstruction have a higher incidence of lateral meniscal tears and less severe chondral changes when compared with patients undergoing late ACL reconstruction. Older patients likely have a higher incidence of chondral and meniscal pathology compared with younger patients. METHODS: A retrospective chart review of a single surgeon's ACL practice over 20 years was performed. A surgical data packet was used to record patient demographics, location, grade, and number of chondral injuries as well as location and pattern of meniscal injuries at the time of ACL reconstruction. Patients (N = 709) were divided into three subgroups according to their time from injury to surgery; acute (less than 4 weeks, N = 121), subacute (4 to 8 weeks, N = 146), and chronic (8 weeks or more, N = 442). RESULTS: Older patients had a higher incidence of more severe chondral grade and number of chondral injuries at the time of ACL reconstruction. Patients undergoing surgery more than 8 weeks after injury had a statistically significant more severe chondral grade in the medial compartment when compared with those that had surgery less than 8 weeks after injury. A similar observation was not found in the lateral compartment. With regard to meniscal pathology, full-thickness medial meniscal tears were likely to be bucket-type tears regardless of the chronicity of the injury. Similarly, full-thickness lateral meniscal tears were more often flap-type tears independent of the time interval between injury and surgery. Partial-thickness tears were common both medially and laterally. CONCLUSIONS: Patient's age and chronicity of ACL tear greater than 8 weeks are both significant factors in medial compartment chondral pathology. Patients with delayed reconstruction may have greater associated pathology.

Interval arthrometric comparison of anterior cruciate ligament reconstruction using bone-patellar tendon-bone autograft versus allograft: do grafts attenuate within the first year postoperatively?

BACKGROUND: There is little information regarding the incremental changes in the postoperative laxity of patellar tendon (PT) autografts versus allografts in anterior cruciate ligament (ACL) reconstruction. HYPOTHESES: (1) There would be no significant increase in laxity between 6 weeks and 1 year postoperatively with PT autografts or allografts, (2) there would be no significant difference in laxity between PT autografts and allografts, (3) there would not be a significant difference in laxity between nonirradiated and low dose-irradiated PT allograft tissues, and (4) the physical examination findings would correlate with the instrumented laxity outcomes. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: A retrospective review of 238 ACL-deficient patients who underwent single-incision endoscopic ACL reconstruction with a PT autograft (n = 132) or allograft (n = 106; 58 irradiated and 48 nonirradiated) from a single surgeon was made looking at data from preoperatively and from 6 weeks to 1 year postoperatively. The objective measurements of ligament integrity included range of motion, Lachman test, pivot-shift test, and KT-1000 arthrometer instrumented laxity examination. Failure was defined as arthrometric side-to-side differences (maximum manual difference) ≥3 mm or a positive pivot shift. Statistical significance was defined as P < .05. RESULTS: There were no differences in postoperative examination findings or instrumented laxity between PT autografts and allografts (irradiated or nonirradiated) in either subgroup. The postoperative improvement based on the Lachman examination, pivot-shift test, and arthrometric data in all study groups was significant (P < .001) in 98% (autograft: n = 130; allograft: n = 104) of patients, and arthrometric failure correlated with failure by physical examination. There was no significant change in graft laxity, as measured by KT-1000 arthrometer, from 6 weeks to 1 year postoperatively for 98% of patients. Finally, there was no statistical correlation in instrumented laxity results for either the autograft or allograft group with reference to age, gender, concurrent meniscectomy, meniscal repairs, interval to surgery, postoperative patellar pain, time to surgery, or irradiated versus nonirradiated allograft. CONCLUSION: Laxity is not increased after the initial 6 weeks for either PT allograft or autograft constructs during the first postoperative year. There was no correlation between age, gender, concomitant injury, interval to surgery, or radiation of the graft with instrumented laxity results. Furthermore, our arthrometric data paralleled our clinical findings of stability at follow-up.

Hip osseous morphology using computer navigation and plain radiographs.

In this study, we used 3-dimensional analysis to comprehensively map the osseous morphology of the acetabulum. Human cadaveric specimens were dissected to the joint capsule for computer navigation analysis. Data points outlining acetabular anatomy-determined using optical sensors-were translated into graphical environments. A clock face template was laid over the transverse plane to determine the projections of acetabular arcs onto the transverse plane. A custom-written software program was used to compute the resulting surface area and was applied to the acetabular articular surface and the fossa. Two independent observers performed all measurements. Sixteen hips were included. Lateral center edge angle was 36.2° and femoral neck shaft angle was 131°. Mean arc lengths of the acetabular fossa from 3 o'clock (anterior) to 9 o'clock (posterior) were 26, 28, 28, 30, 29, 28, and 27 mm at 3, 2, 1, 12, 11, 10, and 9 o'clock, respectively. The smallest aspect of the acetabulum is the anterior aspect, and the largest is the superior (12 o'clock); the size increases progressively from anterior to superior. In most cases, the superior arc length, or sourcil, corresponds to the 2 o'clock position, and thus the lateral center edge angle may not necessarily correspond to the lateral aspect of the acetabulum.

Hip pain in active patients: what you may be missing.

When a patient who's physically active complains of hip pain, don't be too quick to label it a "hip pointer" that requires time and rest to heal. Consider this more nuanced-and effective-approach.

Open versus arthroscopic distal clavicle resection.

PURPOSE: The purpose of this systematic review was to critically evaluate the available literature in an attempt to compare the outcome of open versus arthroscopic distal clavicle resection in the treatment of acromioclavicular joint pathology. METHODS: From January 1966 to December 2008, Medline was searched for the following key words: "acromioclavicular joint arthritis," "acromioclavicular osteolysis," "distal clavicle excision," "acromioclavicular joint excision," "Mumford," and "clavicle." Inclusion criteria included studies that compared the outcome of open versus arthroscopic distal clavicle resection. Studies that could not be translated into the English language or were not published in a peer-reviewed journal were excluded. Data were abstracted from the studies, including patient demographics, surgical procedure, rehabilitation, strength, range of motion, and clinical scoring system. RESULTS: Seventeen studies met the inclusion criteria, including 2 Level II studies, 1 Level III and 14 Level IV studies. Arthroscopic distal clavicle excision results in more "good" or "excellent" outcomes compared with the open procedure. Both arthroscopic techniques result in success rates in excess of 90%, with the direct procedure permitting a quicker return to athletic activities. Performing distal clavicle excision in conjunction with either subacromial decompression or rotator cuff repair also has a high degree of success. A trend toward more "poor" results is seen when distal clavicle excision is performed in patients with post-traumatic acromioclavicular instability or in Workers' Compensation patients. CONCLUSIONS: Our analysis suggests that among patients undergoing distal clavicle excision for acromioclavicular joint pathology, those having an arthroscopic procedure, specifically through the direct approach, can expect a faster return to activities while obtaining similar long-term outcomes compared with the open procedure. LEVEL OF EVIDENCE: Level III, systematic review.

Surgical management of articular cartilage defects in the knee.

The treatment of isolated cartilage lesions of the knee is based on several underlying principles, including a predictable reduction in the patient's symptoms, improvements in function and joint congruence, and prevention of progressive damage. Surgical options for cartilage restoration are described as palliative treatments, such as débridement and lavage; reparative, such as marrow stimulation techniques; or restorative, such as osteochondral grafting and autologous chondrocyte implantation. The choice of an appropriate treatment should be made on an individual basis, with consideration for the patient's specific goals (such as pain reduction or functional improvement), physical demand level, prior treatment history, lesion size and location, and a systematic evaluation of the knee that considers comorbidities, including alignment, meniscal status, and ligament integrity. It is important for the physician to be familiar with the indications, surgical techniques, and clinical outcomes of the available treatment options for chondral defects of the knee.

Does the literature confirm superior clinical results in radiographically healed rotator cuffs after rotator cuff repair?

PURPOSE: Because recurrent or persistent defects in the rotator cuff after repair are common, we sought to clarify the correlation between structural integrity of the rotator cuff and clinical outcomes through a systematic review of relevant studies. METHODS: Medline, CINAHL (Cumulative Index to Nursing and Allied Health Literature), and the Cochrane Central Register of Controlled Trials were searched for all literature published from January 1966 to December 2008 that used the key words shoulder, rotator cuff, rotator cuff tear, rotator cuff repair, arthroscopic, integrity, healed, magnetic resonance imaging (MRI), computed tomography arthrography (CTA), and ultrasound. The inclusion criteria were studies (Levels I to IV) that reported outcomes after arthroscopic rotator cuff repair in healed and nonhealed repairs based on ultrasound, CTA, and/or MRI. Exclusionary criteria were studies that included open repair or subscapularis repair and studies that did not define outcomes based on healed versus nonhealed but rather used another variable (i.e., repair technique). Data were abstracted from the studies including patient demographics, tear characteristics, surgical procedure, rehabilitation, strength, range of motion, clinical scoring systems, and imaging studies. RESULTS: Thirteen studies were included in the final analysis: 5 used ultrasound, 4 used MRI, 2 used CTA, and 2 used combined CTA/MRI for diagnosis of a recurrent tear. Statistical improvement in patients who had an intact cuff at follow-up was seen in Constant scores in 6 of 9 studies; in University of California, Los Angeles scores in 1 of 2 studies; in American Shoulder and Elbow Surgeons scores in 0 of 3 studies; and in Simple Shoulder Test scores in 0 of 2 studies. Increased range of motion in forward elevation was seen in 2 of 5 studies and increased strength in forward elevation in 5 of 8 studies. CONCLUSIONS: The results suggest that some important differences in clinical outcomes likely exist between patients with healed and nonhealed rotator cuff repairs. Further study is needed to conclusively define this difference and identify other important prognostic factors related to clinical outcomes. LEVEL OF EVIDENCE: Level IV, systematic review.

Arthroscopic stabilization for first-time versus recurrent shoulder instability.

PURPOSE: The purpose of this study was to systematically review the evidence on the outcomes of arthroscopic repair for anterior shoulder instability in first-time dislocators when compared with patients with recurrent instability. METHODS: We designed a systematic review with a specific methodology to investigate the outcomes of surgery for those with only a first-time dislocation versus those who underwent surgery after multiple instability events. We performed a literature search from January 1966 to December 2008 using Medline, CINAHL (Cumulative Index to Nursing and Allied Health Literature), and the Cochrane Central Register of Controlled Trials. Key words included the following: first time, primary shoulder, or recurrent shoulder instability, shoulder dislocation, Bankart repair, arthroscopic Bankart repair, and labral repair. The inclusion criteria were cohort studies (Level I to II) that evaluated the outcomes of patients undergoing arthroscopic stabilization after the first dislocation or multiple recurrent episodes. Studies that lacked a comparison group or were retrospective (Level III studies or higher) were excluded. RESULTS: There were 15 studies that met the inclusion criteria and were included in the final analysis: 5 in the first-time dislocation group and 10 in the recurrent instability group. Study design, patient demographics, mean number of dislocations, surgical technique, and rehabilitation protocol, as well as subjective and objective outcome measures, were recorded. CONCLUSIONS: There were no differences in recurrence or complication rate among patients undergoing surgery after the primary dislocation when compared with those undergoing surgery after multiple recurrent episodes. Clinical outcome measures significantly improved within all independent studies from preoperatively to postoperatively. However, because of variation in the outcome measurement tools used, no direct comparison between the study groups could be performed. Additional randomized controlled studies are needed to compare the functional outcome, quality of life, and ability to return to preinjury activity level among patients undergoing early versus delayed repair for anterior shoulder instability.

Lateral hip pain in an athletic population: differential diagnosis and treatment options.

CONTEXT: Historically, the term greater trochanteric pain syndrome has been used to describe a spectrum of conditions that cause lateral-sided hip pain, including greater trochanteric bursitis, snapping iliotibial band, and/or strains or tendinopathy of the abductor mechanism. Diagnosis of these conditions may be difficult because clinical presentations are variable and sometimes inconclusive. Especially difficult is differentiating intrinsic pain from pain referred to the greater trochanteric region. The purposes of this article are to review the relevant anatomy and pathophysiology of the lateral hip. EVIDENCE ACQUISITION: Data were collected through a thorough review of the literature conducted through a MEDLINE search of all relevant papers between 1980 and January 2010. RESULTS: Recent advances in imaging and an improved understanding of pathomechanics have helped to guide the evaluation, diagnosis, and appropriate treatment for patients presenting with lateral hip pain. CONCLUSION: Various diagnostic tools and treatment modalities can be used to effectively manage the athletic patient presenting with lateral hip pain.

Posterior hip pain in an athletic population: differential diagnosis and treatment options.

CONTEXT: Posterior hip pain is a relatively uncommon but increasingly recognized complaint in the orthopaedic community. Patient complaints and presentations are often vague or nonspecific, making diagnosis and subsequent treatment decisions difficult. The purposes of this article are to review the anatomy and pathophysiology related to posterior hip pain in the athletic patient population. EVIDENCE ACQUISITION: Data were collected through a thorough review of the literature via a MEDLINE search of all relevant articles between 1980 and 2010. RESULTS: Many patients who complain of posterior hip pain actually have pain referred from another part of the body-notably, the lumbar spine or sacroiliac joint. Treatment options for posterior hip pain are typically nonoperative; however, surgery is warranted in some cases. CONCLUSIONS: Recent advancements in the understanding of hip anatomy, pathophysiology, and treatment options have enabled physicians to better diagnosis athletic hip injuries and select patients for appropriate treatment.

Does the literature support double-row suture anchor fixation for arthroscopic rotator cuff repair? A systematic review comparing double-row and single-row suture anchor configuration.

PURPOSE: The purpose of this study was to compare the clinical outcome of single-row (SR) and double-row (DR) suture anchor fixation in arthroscopic rotator cuff repair with a systematic review of the published literature. METHODS: We searched all published literature from January 1966 to December 2008 using Medline, CINAHL (Cumulative Index to Nursing and Allied Health Literature), and the Cochrane Central Register of Controlled Trials for the following key words: shoulder, rotator cuff, rotator cuff tear, rotator cuff repair, arthroscopic, arthroscopic-assisted, single row, double row, and transosseous equivalent. The inclusion criteria were cohort studies (Levels I to III) that compared SR and DR suture anchor configuration for the arthroscopic treatment of full-thickness rotator cuff tears. The exclusion criteria were studies that lacked a comparison group, and, therefore, case series were excluded from the analysis. RESULTS: There were 5 studies that met the criteria and were included in the final analysis: 5 in the SR group and 5 in the DR group. Data were abstracted from the studies for patient demographics, rotator cuff tear characteristics, surgical procedure, rehabilitation, range of motion, clinical scoring systems, and imaging studies. CONCLUSIONS: There are no clinical differences between the SR and DR suture anchor repair techniques for arthroscopic rotator cuff repairs. At present, the data in the published literature do not support the use of DR suture anchor fixation to improve clinical outcome, but there are some studies that report that DR suture anchor fixation may improve tendon healing. LEVEL OF EVIDENCE: Level III, systematic review of Levels I to III studies.

Development of a new model for rotator cuff pathology: the rabbit subscapularis muscle.

BACKGROUND AND PURPOSE: The New Zealand white rabbit subscapularis tendon passes under a bony arch to insert on the lesser tubercle of the humerus in a manner analogous to the supraspinatus tendon in humans. We assessed whether this unique anatomy may provide a new animal model of the shoulder to improve our understanding of rotator cuff pathology. METHODS: The dimensions of the rotator cuff insertions (subscapularis, supraspinatus, and infraspinatus) were measured on 10 fresh frozen cadaveric New Zealand white rabbit shoulders. Mechanical testing was performed on 8 fresh frozen subscapularis insertions (4 matched pairs). Video analysis of the gait cycle was performed on 2 live animals. RESULTS: The origins, insertions, and innervations of the rabbit rotator cuff musculature are analogous to those in humans. However, the rabbit acromion is a rudimentary structure with only the infraspinatus and teres minor muscles passing beneath. Furthermore, at the point where the infraspinatus passes under the arch, it is muscular rather than tendinous. The anterior aspect of the glenohumeral joint contains an additional bony tunnel with its boundaries being the tuberculum supraglenoidale laterally, the coracoideus process superiorly, the tuberculum infraglenoidale inferiorly, and the coracobrachialis muscle medially. The origin of the rabbit subscapularis muscle resides on the anterior scapula. The subscapularis tendon then traverses this bony tunnel prior to its insertion on the lesser tubercle of the humerus. Video analysis and anatomic dissections confirmed excursion of the subscapularis tendon within this bony tunnel throughout the gait cycle. The subscapularis footprint on the proximal humerus measured 6.8 mm (SD 0.29) x 2.5 mm (SD 0.17). Mechanical testing of the subscapularis tendon showed the stiffness to range from 57 to 117 N/mm (SD 23). Ultimate yield ranged from 88 to 215 N (SD 518). The elastic modulus of the rabbit tendon was 56 MPa. 6 of the 8 subscapularis tendons failed at the tendon mid-substance; the other 2 failed at the bony insertion. INTERPRETATION: The unique anatomic architecture and the mechanical characteristics of the rabbit subscapularis muscle provide an opportunity to improve our understanding of rotator cuff pathology.