Tyson K. Cobb

Total Elbow Arthroplasty as Primary Treatment for Distal Humeral Fractures in Elderly Patients

We retrospectively reviewed the results of primary total elbow arthroplasty for the treatment of an acute fracture of the distal aspect of the humerus in twenty consecutive patients (twenty-one elbows) who had a mean age of seventy-two years (range, forty-eight to ninety-two years) at the time of the injury. The patients were managed between November 1982 and October 1992. The presence of rheumatoid arthritis in nine patients (ten elbows) influenced the choice of treatment. The mean interval between the injury and the total elbow arthroplasty was seven days (range, one to twenty-five days). The mean duration of postoperative hospitalization was seven days (range, four to thirteen days). The mean duration of follow-up was 3.3 years (range, three months to 10.5 years). All patients were followed for a minimum of two years or until the time of death; the duration of follow-up was less than two years for three patients who died. None of the patients were lost to follow-up. Twenty implants were intact at the latest follow-up examination. One patient had a revision total elbow arthroplasty twenty months after the index procedure because of a fracture of the ulnar component sustained in a fall on the outstretched arm. On the basis of the Mayo elbow performance score, fifteen elbows had an excellent result and five had a good result; there were inadequate data for one elbow. There were no fair or poor results. The mean arc of flexion was 25 to 130 degrees. There was no evidence of loosening on the radiographs. Postoperative complications included fracture of the ulnar component in one patient, ulnar neurapraxia in three, and reflex sympathetic dystrophy in one. The results suggest that total elbow arthroplasty can be an alternative form of treatment of a severely comminuted fracture of the distal aspect of the humerus in older patients even in the presence of rheumatoid arthritis. This procedure is not an alternative to osteosynthesis in younger patients.

The elevated-rim acetabular liner in total hip arthroplasty: relationship to postoperative dislocation.

Although an acetabular component with an elevated rim is thought to improve the postoperative stability of a total hip prosthesis, the actual clinical value has not yet been demonstrated. To address this question, we reviewed the results of 5167 total hip arthroplasties that had been performed at our institution from April 1, 1985, through December 31, 1991. The prostheses included 2469 acetabular components with an elevated-rim liner (10 degrees of elevation) and 2698 with a standard liner. The cumulative probability of dislocation was estimated as a function of time since the operation with use of the Kaplan-Meier survivorship method. Forty-eight of the 2469 hips that had the elevated-rim acetabular liner dislocated within two years, compared with 101 of the 2698 hips that had the standard acetabular liner. The two-year probability of dislocation was 2.19 per cent for the hips with the elevated-rim liner and 3.85 per cent for those with the standard liner (p = 0.001). A similar trend was seen at five years; however, because of a smaller sample the difference was not significant. Increased stability at two years was also demonstrated for the hips with the elevated-rim liner when the hips were analyzed according to the operative approach, the mode of fixation, the sex of the patient, and the type of total hip arthroplasty (primary or revision). Although these data demonstrate improved stability after total hip arthroplasty when an elevated liner is used, particularly in hips that are at greater risk for dislocation of the prosthesis, the long-term effect of this elevated liner on wear and loosening remains unknown but is of considerable concern. The elevated liner deserves additional study to clarify its effect on wear and loosening.

Outcome of reoperation for carpal tunnel syndrome

One hundred thirty-one patients with reoperation for carpal tunnel syndrome were followed for a mean of 11 years. Reoperation failed in 15 patients, necessitating a third operation. Satisfaction, symptom severity, and functional status scores were assessed with a standardized questionnaire in the other 116 patients. Patients with normal findings on preoperative nerve conduction studies, those who filed for compensation, and those who had pain in the distribution of the ulnar nerve had significantly worse results. Those with abnormal findings on nerve conduction studies who had not filed for compensation had the best symptom and function scores and satisfaction at latest follow-up examination; those with normal findings on nerve conduction studies who had filed for compensation had the poorest outcome. Although most patients were satisfied with the overall outcome, many reported residual symptoms; in addition to the 15 patients who required a third operation, 22 patients were dissatisfied with the final result.

Lumbrical Muscle Incursion into the Carpal Tunnel During Finger Flexion

Carpal tunnel syndrome is one of the many so-called cumulative trauma disorders thought by some to be related to the performance of repetitive tasks in the work-place. The cause of this disorder is unknown. We have observed lumbrical muscle incursion into the carpal tunnel during finger flexion. This study was conducted to determine the amount of this incursion in normal wrists. Five cadaver upper limbs were analyzed radiographically with radiopaque markers on the flexor retinaculum and the lumbrical muscle origins in four finger positions: full extension, 50% flexion, 75% flexion, and 100% finger flexion. The lumbrical muscle origins were an average of 7.8 mm distal to the carpal tunnel in full finger extension. They moved an average of 14 mm into the carpal tunnel with 50% finger flexion, 25.5 mm with 75% flexion, and 30 mm with 100% flexion. Abnormal lumbrical muscles have been cited as a possible cause of carpal tunnel syndrome. These findings suggest that lumbrical muscle incursion during finger flexion is a normal occurrence and is a possible cause of work-related carpal tunnel syndrome.

The use of topographical landmarks to improve the outcome of agee endoscopic carpal tunnel release

A modified approach to endoscopic carpal tunnel release has been developed and tested in 60 cadaveric specimens by three surgeons using the Agee endoscopic carpal tunnel release system. The modified approach, which includes specific localization of the hook of the hamate, flexor retinaculum, and the superficial palmar arch utilizing topographical landmarks, avoids entry into Guyons canal and injury to the ulnar artery and nerve, median nerve, and common digital nerves. Use of the anatomic approach resulted in significantly superior results. There were fewer incomplete releases, and fewer surgical passes were required, for the inexperienced surgeons. When these anatomic considerations were not included, the learning curve was much steeper. For surgeons planning endoscopic surgical release of the transverse carpal ligament, the described topographical approach improves the technical competence with the procedure and reduces the number of complications and learning curve associated with new procedures. We recommend the use of topographical landmarks and other anatomic considerations during endoscopic carpal tunnel release.

The ulnar neurovascular bundle at the wrist. A technical note on endoscopic carpal tunnel release

The boundaries of Guyon’s canal have recently been redefined by a series of anatomical dissections. These showed that the confines of this space do not extend from the pisiform to the hook of the hamate, as currently accepted. The fascial roof extends radial to the hook of the hamate, which allows the ulnar neurovascular bundle to course radial to the hamate hook. The position of the ulnar nerve and artery is of particular significance for endoscopic carpal tunnel release. Most endoscopic devices are designed to divide the flexor retinaculum just to the radial aspect of the hamate hook. Utilizing cross-sectional analysis of nine cadaver specimens, we found the ulnar artery to course radial to the hamate hook in five and palmar to it in four. Therefore, the ulnar artery may be at greater risk of injury during endoscopic procedures than previously recognized.

Significance of incomplete release of the distal portion of the flexor retinaculum implications for endoscopic carpal tunnel surgery

Endoscopic carpal tunnel release has been shown in recent studies to result in a significant number of incomplete releases of the distal aspect of the flexor retinaculum. The significance of this complication is unknown. To address this question, we measured the amount of carpal arch widening after incomplete and complete release. The mean amount of change in carpal arch width in five cadaveric hands after partial release (all but the distal 4 mm) was 0.74 mm, which was statistically significant. The mean additional change after release of the remaining 4 mm of the flexor retinaculum was 0.12 mm, which was not significant. Incomplete release of the distal 4 mm of the distal aspect of the flexor retinaculum allows carpal arch widening that is no different from that of complete sectioning of the flexor retinaculum in the cadaver limb.

Effect of the elevated-rim acetabular liner on loosening after total hip arthroplasty.

Elevated-rim acetabular liners recently were shown to be associated with improved stability of total hip prostheses in a large clinical series. However, the effect of this design on loosening remains unknown. To address this question, we reviewed the results of 5167 primary and revision total hip arthroplasties that had been performed at our institution from September 1, 1985, through December 31, 1991; 2469 of the acetabular components had an elevated-rim liner (10 degrees of elevation), and 2698 had a standard liner. Five-year follow-up data were available for 1237 hips (174 that had an elevated-rim acetabular liner and 1063 that had a standard acetabular liner). The cumulative probability of revision because of loosening of the implant was estimated as a function of time since the operation with use of the Kaplan-Meier survivorship method. The five-year probability of survival of the acetabular component was 98.8 per cent (95 per cent confidence interval, 97.9 to 99.6 per cent) for the prostheses that had an elevated-rim liner and 98.3 per cent (95 per cent confidence interval, 97.7 to 99.0 per cent) for those that had a standard liner (p = 0.87). The effect of the elevated-rim acetabular liner on the probability of revision because of loosening of the acetabular or the femoral component was analyzed for several subgroups: components inserted with cement, components inserted without cement, primary total hip arthroplasties, revision total hip arthroplasties, male patients, and female patients. With the numbers available, no significant differences were found in the probability of survival of the acetabular or the femoral component in any of the subgroups. Theoretical considerations suggest that the geometric design of the elevated-rim acetabular liner may have biomechanical characteristics that predispose the implant to early loosening. However, our initial review of the results of total hip arthroplasties after a mean follow-up period of five years (range, 0.25 to ten years) failed to demonstrate any difference in the cumulative probability of revision because of loosening of the implant. Continued surveillance is warranted and ongoing.

Aetiology of work-related carpal tunnel syndrome: The role of lumbrical muscles and tool size on carpal tunnel pressures

A cadaveric study was undertaken to investigate the effect of tool size and lumbrical muscle incursion on carpal tunnel pressure during active grip. Active grip was simulated by securing the specimens on an apparatus and loading each of the eight finger flexor tendons with 1 kg each. Carpal tunnel pressures were measured with and without 1- and 2-in. tubing in the hand and before and after removing the lumbrical muscles. Both variables, tool size and lumbrical muscles, were found to have a statistically significant effect on carpal tunnel pressure. Higher pressure changes were found for the 2-in. tubing, compared with 1-in. tubing, but this difference was not statistically significant.

Clinical location of hook of hamate: A technical note for endoscopic carpal tunnel release

Endoscopic carpal tunnel release involves a limited surgical exposure to release the transverse carpal ligament* (TCL).‘** Topographic landmarks can provide valuable reference points to enhance an operation. The hook of the hamate is a useful guide to the ulnar (safe) border of the carpal canal but can be difficult to palpate. Kaplan’s cardinal line has been used to estimate the position of the hook of the hamate and the superficial palmar arch. However, the accuracy of this technique is questionable because it is based on a moving reference point, the web space of the thumb. We report a technique to localize the position of the hook of the hamate and define key relationships of clinical importance for endoscopic carpal tunnel release.