The influence of tendon length and fit on the strength of a tendon-bone tunnel complex. A biomechanical and histologic study in the dog.

Using a dog model, we examined the influence of tendon length and fit within a bone tunnel on the pull-out strength of a tendon-bone tunnel complex at 6 weeks after fixation. Fourteen adult mongrel dogs (weight, 25 to 30 kg) underwent bilateral hindlimb surgery in which the extensor digitorum longus tendon was transplanted into an extraarticular metaphyseal bone tunnel. Our findings demonstrated that pull-out strength at 6 weeks was enhanced by increasing the length of tendon within the tunnel. The average load to failure with 1 cm of tendon within the tunnel was 153.7 +/- 78.6 N, compared with 265.5 +/- 93.3 N for the specimens with 2 cm of tendon in the tunnel. Tendon fit within the tunnel was also found to be important. The average load to failure when a tendon was placed in a 4.2-mm diameter tunnel was 301 +/- 61 N at 6 weeks. The average load to failure when the tendon was placed within a 6-mm diameter tunnel was 228 +/- 65 N. These differences were statistically different. Histologically, the interface between the tendon and bone appeared to be most mature when there was intimate bone-to-tendon contact. These data suggest that maximizing tendon length within a bone tunnel and minimizing tendon-tunnel diameter mismatch will maximize the strength of a tendon-bone tunnel complex at 6 weeks.

Axillary nerve temperatures during radiofrequency capsulorrhaphy of the shoulder.

PURPOSE: The purpose of this study was to determine the temperatures along the course of the axillary nerve during radiofrequency (RF) capsulorrhaphy of the shoulder in a cadaver model. The hypothesis of this project was that temperatures capable of damaging neural tissue would be recorded during simulated RF capsulorrhaphy. TYPE OF STUDY: Basic science evaluation. METHODS: This study used 9 fresh-frozen cadaver shoulder capsules removed en bloc along with the underlying axillary nerve and soft tissue. The axillary nerve was instrumented with 4 thermocouples placed along the course of the nerve (2 thermocouples anterior and 2 posterior to the 6 o'clock position, spaced 7 mm apart). Each of the specimens underwent RF thermal capsulorrhaphy during which the temperature at each of the thermocouple positions was continuously recorded. RESULTS: The average of the maximum temperature at each of the 4 positions measured along the course of the axillary nerve were 52.2 +/- 18.0 degrees C at the most anterior place probed, 45.8 +/- 5.44 degrees C (mid anterior), 44.5 +/- 8.7 degrees C (mid posterior), and 42.8 +/- 10.1 degrees C at the most posteriorly positioned probe. Two specimens had a maximum temperature greater than the 67 degrees C set point of the device, and 7 specimens had a maximum temperature greater than 45 degrees C in at least 1 thermocouple position. CONCLUSIONS: This study shows that heating of the axillary nerve can occur during RF capsular shrinkage of the shoulder and may potentially reach levels that can damage neural tissue.

Axillary nerve injury after thermal capsular shrinkage of the shoulder.

The purpose of this study was to evaluate 4 cases in which axillary nerve injury was observed after radiofrequency capsular shrinkage of the shoulder. These cases were used to evaluate the clinical circumstances under which axillary nerve injury occurred, the time frame over which these injuries recovered, and the ultimate outcome observed in these patients. The case histories of each of these 4 patients were carefully evaluated. In 2 of the 4 cases, purely sensory findings were found, and in 2 cases both sensory and motor injuries occurred. In each case the inferior axillary recess was treated using the Oratech Interventions Tac-S probe. The authors conclude that injury to the axillary nerve during this procedure is possible and postulate that heat penetration through the capsule to the nerve is the most likely cause of injury.

Pitfalls associated with fixation of osteochondritis dissecans fragments using bioabsorbable screws.

The purpose of this study was to evaluate 2 cases in which bioabsorbable screw fixation for an osteochondritis dissecans lesion of the femoral condyle resulted in complications necessitating the need for secondary surgery. We reviewed the case history of these patients and described the circumstances under which the bioabsorbable screws were used, the events leading to the need for secondary surgery, and the ultimate outcome. In the 2 cases presented, these implants were found to retain their mechanical stiffness for many months. This resulted in articular damage in 1 case after the treated lesion failed to heal. In the second case, screw breakage 8 months after implantation resulted in it becoming a loose body, which required removal during a second arthroscopic procedure. We conclude that these implants retain their mechanical properties for many months and cannot be relied on to degrade quickly. If a treated lesion fails to heal, these implants can cause mechanical problems due to their retained structural properties.

Treatment of symptomatic glenoid loosening following unconstrained shoulder arthroplasty.

Nine patients with symptomatic glenoid loosening were identified and ultimately underwent surgical revision. Preoperative assessment demonstrated that pain, decreased range of motion, and functional disability were common features. A painful clunking sensation with forward elevation of the arm was noted in four of the nine patients. At surgical revision, a grossly loose glenoid component was found in all cases and removed. Seven of the nine patients underwent revision using another cemented glenoid component, and two patients were left with a hemiarthroplasty due to glenoid bone deficiency. Results following revision surgery demonstrated increased range of motion, decreased pain, and increased functional ability with good overall patient satisfaction in seven of nine patients. Two patients in whom revision glenoid components were implanted were considered failures due to recurrent loosening. Although revision of the glenoid component is often technically feasible, recurrent loosening may occur. Revision to a hemiarthroplasty may be an acceptable alternative to glenoid replacement.

Validation of the lift-off test and analysis of subscapularis activity during maximal internal rotation.

We used electromyographic analysis to determine the muscle activity of the shoulder muscles during the lift-off test and during resisted internal rotation. The activity in the upper and lower subscapularis muscle during a lift-off test from the region of the midlumbar spine was approximately 70% of maximal voluntary contraction. This level was significantly higher than for all the other muscles tested (P < 0.05). The lift-off test with the hand placed in the region of the midlumbar spine resulted in one-third more electromyographic activity in the subscapularis muscle than when the test was modified and performed with the hand at the buttocks region. A resisted lift-off test resulted in higher activities in all the muscles, but only a small increase in the pectoralis major muscle. The pectoralis major muscle was significantly more active during resisted internal rotation with the arm in front of the body. Comparison of activity in the upper subscapularis with that in the lower subscapularis muscle showed no significant differences during any of the tests. This study documents the importance of the subscapularis muscle during the lift-off test and suggests that other potential internal rotators of the humerus have a limited role in maintaining internal rotation when the arm is placed behind the back.

Subscapularis tendon disruption after Bankart reconstruction for anterior instability.

After undergoing a Bankart repair with a subscapularis tendon and capsular incising technique, four patients were identified who had failure of their subscapularis tendon repair. All had a traumatic event or injury to their shoulder between 1 day and 4 months after operation. The patients presented with findings including recurrent instability, weakness in internal rotation, an abnormal liftoff test, and increased external rotation of the affected extremity. Surgical exploration demonstrated failure of the Bankart repair in two cases in addition to failure of the subscapularis tendon repair in all four. In one patient magnetic resonance imaging was diagnostic of subscapularis tendon disruption. After reoperation was performed, stability was achieved in three of four patients, return of normal internal rotation strength in two, and a normal liftoff test in two. Prompt reexploration and repair of the subscapularis tendon-capsule complex is recommended.

Revision of failed prosthetic anterior cruciate ligament reconstruction.

Revision of failed prosthetic anterior cruciate ligament reconstructions will continue to be necessary as previously placed prosthetic devices fail with time. These patients often present with recurrent instability, pain, swelling, or effusions. Graft rupture and the generation of particulate debris are common causes of these symptoms. To effectively treat these patients requires careful preoperative evaluation and planning. Operative treatment includes removing the prosthesis and metal fixation devices, evaluating femoral and tibial bone stock, and determining adequacy of previous tunnel position. Staging of the operation may be a necessity if significant bone loss or poor tunnel position on either the femoral or tibial side requires bone grafting. The use of an autogenous bone-patellar tendon-bone graft is suggested and has proven to be effective in restoring knee stability in these revision cases. The ultimate outcome following revision of failed prosthetic ligaments may be limited by associated intraarticular pathology often seen in this patient population.

Arthroscopic evaluation and treatment of shoulder instability.

The use of the arthroscope for shoulder instability has improved our understanding of normal and pathologic shoulder anatomy. We must emphasize, however, that the majority of shoulder problems can be accurately diagnosed with a thorough history and good physical examination. The arthroscope is helpful, however, to confirm a clinical diagnosis or assist in making a diagnosis in difficult or complex pathologic findings. Further, as our surgical techniques and understanding of shoulder instability improve, more pathologic entities about the shoulder become amenable to arthroscopic surgical procedures. We must emphasize that most of these arthroscopic procedures are technically demanding and significant learning curves exist. These procedures should be undertaken only by physicians who have excellent arthroscopic skills and are comfortable recognizing normal and pathologic arthroscopic anatomy of the shoulder.

Arthroscopic removal of loose bodies of the elbow.

Arthroscopy of the elbow has proven to have a diagnostic and therapeutic benefit. Removal of loose bodies and a thorough evaluation of associated intra-articular pathologies are possible without arthrotomy. The authors have found this procedure to be safe and effective in the treatment of loose bodies of the elbow and other associated pathologies.

Particle-induced synthesis of collagenase by synovial fibroblasts: an immunocytochemical study.

The response of synoviocytes to wear particles has been implicated in several orthopaedic pathologies, including the synovitis associated with the failure of synthetic anterior cruciate ligament (ACL) replacements. To study the interactions of particles with synovial fibroblasts at the level of the individual cell, we employed immunocytochemistry, with use of antiserum, to lapine interstitial collagenase. Cultures of the HIG-82 lapine synovial cell line showed only weak immunofluorescence under resting conditions. Incubation with phorbol myristate acetate or autocrine factors known as cell-activating factors (CAFs) induced marked changes in morphology and intense immunofluorescence. This technique then was used to study the effects of standard particles of latex and of particles generated from two prosthetic ACL materials, Dacron and carbon. Internalized particles of latex, Dacron, and carbon all induced collagenase. Particles of latex that were too large for endocytosis failed to induce collagenase, whereas particles of carbon and, in particular, Dacron that remained extracellular, still provoked considerable synthesis of collagenase. Thus, both the size and the physical properties of these materials influence their ability to activate synoviocytes. Certain cells that appeared by visual inspection to contain no particles nevertheless produced collagenase when in co-culture with cells that did contain particles. This is consistent with earlier biochemical data showing that phagocytosis, in addition to inducing collagenase, also provokes the release of CAFs, which then activate additional cells in the culture. More rarely, cells were identified which, although containing particles, did not stain positively for collagenase.(ABSTRACT TRUNCATED AT 250 WORDS)

Revision anterior cruciate ligament surgery: causes of graft failure and technical considerations of revision surgery.

The frequency of revision ACL surgery is sure to become more common as the number of primary intraarticular reconstructions increase. Identifying the potential causes of failure through a detailed history, physical examination, and radiographic evaluation is of paramount importance prior to planning a revision surgery if the repetition of errors is to be avoided.

A clinical and comparative biomechanical evaluation of proximal femoral osteotomy fixation in children.

This study compared the biomechanical characteristics of a 90 degrees infant blade plate construct and anteriorly applied 120 degrees angled plate construct in response to an axial compression load. The blade plate construct stiffness was three times greater than the angled plate construct (238.9 vs 85.7 N/deg). Four degrees failure load was also significantly higher for the blade plate. Despite inferior biomechanical characteristics, the 120 degrees angled plate functioned very satisfactorily in a retrospective clinical review of 21 proximal femoral varus osteotomies. The authors conclude that the 120 degrees angled plate has practical benefits in terms of ease of insertion and intraoperative adjustability which may outweigh its biomechanical inferiority.

A long-term study on defect filling and bone ingrowth using a canine fiber metal total hip model.

When performing primary and revision total hip arthroplasty (THA), bone defects are often encountered. At present, grafting osseous defects with autogeneic bone is a common means of treatment. In this study, defects in bone were created in the femora and acetabula of dogs being treated with cementless THA with a fiber metal implant (Group A) or a hydroxyapatite tricalcium phosphate (HA/TCP) sprayed implant (Group B). The following methods of defect filling were compared: (1) leaving defects unfilled, (2) filling with autogeneic bone graft, (3) filling with a 50:50 mixture of autograft and a biphasic ceramic composed of HA/TCP, and (4) filling with a collagen-HA/TCP-bone marrow mixture. Analysis of defect healing and the extent of ingrowth into the overlying fiber metal, at defect sites and sites distant from defects, was made at six, 12, and 24 weeks postimplantation. Defect healing was enhanced at six and 12 weeks in all grafted groups when compared with ungrafted controls. Bone ingrowth into the porous fiber metal overlying the defects was not significantly affected by grafting the defects, compared with the ungrafted defects. The extent of bone ingrowth into the fiber metal acetabular implant at sites away from the defects increased during the entire study. In contrast, the extent of bone ingrowth on the femoral side was maximal at 12 weeks. The HA/TCP coating enhanced ingrowth into the acetabular component at 12 weeks, compared with the uncoated prosthesis, but did not enhance ingrowth on the femoral side. The data from this study demonstrate that defect healing is enhanced with graft materials. However, this does not necessarily result in increased ingrowth into porous surfaces overlying osseous defects. General bone ingrowth and ingrowth at defect sites at 12 weeks postimplantation can be enhanced on the acetabular side with the use of HA/TCP-sprayed implants. However, no positive effect is seen with the use of an HA/TCP-sprayed femoral implant.

Eosinophilic granuloma. The management of solitary lesions of bone.

Solitary eosinophilic granuloma (EG) lesions of bone can represent diagnostic and treatment dilemmas for the orthopedic surgeon. A retrospective review of one institution's experience with isolated EG skeletal lesions over a 30-year period was undertaken. Solitary lesions responded well to most treatment modalities (e.g., curettage, excision, and irradiation) and infrequently resulted in functional impairment. While EG involvement in bone can be a manifestation of a systemic histiocytosis, single-focus skeletal involvement appears to be a benign pathophysiologic process.