Biomechanical effects of operative nerve mobilization and transposition in a canine ulnar nerve model

The effect of operative technique on ulnar nerve strain following surgery for cubital tunnel syndrome

BACKGROUND

The aim of this study is to compare the amount of strain on the ulnar nerve based on elbow position after in situ release, subcutaneous transposition, submuscular transposition, and medial epicondylectomy.

METHODS

Six matched cadaver upper extremity pairs underwent ulnar nerve decompression, transposition in a sequential fashion, while five elbows underwent medial epicondylectomy. A differential variable reluctance transducer (DVRT) was placed in the ulnar nerve. An in situ release, a subcutaneous transposition, and a submuscular transposition were performed sequentially with the strain being measured after each procedure in neutral, full elbow flexion, and extension positions. The strain was then averaged and compared for each procedure. Five cadavers underwent medial epicondylectomy and were similarly tested.

RESULTS

After the in situ release, there was no statistically significant change in strain in either flexion or extension. After a subcutaneous transposition, there was a statistically significant decrease in strain in full elbow flexion but not in extension. Similarly after a submuscular transposition, there was a statistically significant decrease in strain in full flexion but not in extension. There was not a statistically significant change in strain with medial epicondylectomy.

CONCLUSION

An in situ release of the ulnar nerve at the elbow may relieve pressure on the nerve but does not address the problem of strain which may be the underlying pathology in many cases of ulnar neuropathy at the elbow (UNE). Transposition of the ulnar nerve anterior to the medial epicondyle addresses the problem of strain on the ulnar nerve. In addition, it does not create an increased strain on the ulnar nerve with elbow extension.

The Management of Cubital Tunnel Syndrome

Symptomatic cubital tunnel syndrome is a condition that frequently prompts patients to seek hand surgical care. Although cubital tunnel syndrome is readily diagnosed, achieving complete symptom resolution remains challenging. This article reviews related anatomy, clinical presentation, and current management options for cubital tunnel syndrome with an emphasis on contemporary outcomes research.

Comparison of transposition techniques to reduce gap associated with high ulnar nerve lesions

PURPOSE

To determine in a cadaveric model which of 3 anterior transposition techniques allows for maximum gap reduction for high ulnar nerve lesions.

METHODS

Six fresh-frozen human adult upper extremity cadaveric transhumeral specimens were used. We anchored the ulnar nerve to bone 10 cm proximal and distal to the medial epicondyle along its exact course while keeping the elbow in 30° flexion as the baseline measurement. We then used a thick suture to mimic and measure the exact course of the nerve between the pins in varying elbow positions. The nerve was then transposed first subcutaneously, then intramuscularly, and then submuscularly while taking exact measurements of the distance the nerve had to travel in varying degrees of elbow flexion for each transposition method. We performed comparative analysis to analyze gap reduction with respect to transposition method and elbow position.

RESULTS

Transposing the ulnar nerve reduced the repair gap required to cross the elbow regardless of transposition technique. When comparing individual techniques, however, the greatest gap reduction was achieved by intramuscular, followed by submuscular and finally subcutaneous transposition. A maximum gap reduction of 25 mm (average, 23 mm) was achieved using intramuscular transposition with the elbow in 90° flexion. Subcutaneous transposition actually increased the repair gap when the elbow was in an extended position.

CONCLUSIONS

An intramuscular transposition with the elbow in 90° flexion provided the best gap reduction. However, post-neurorrhaphy mobilization may compromise repair site integrity and vascularity if elbow flexion is required to achieve a primary repair, and these factors should be considered carefully when planning treatment.

CLINICAL RELEVANCE

This study provides guidance on techniques to reduce nerve gap for primary repair of the ulnar nerve at the elbow using transposition and elbow flexion.

Outcomes following modified oblique medial epicondylectomy for treatment of cubital tunnel syndrome

PURPOSE

To quantify and define objective and patient-rated outcomes after our modification of medial epicondylectomy for the treatment of cubital tunnel syndrome. Although medial epicondylectomy has been previously studied, data are lacking regarding elbow-specific outcomes after our technique that aims to minimize complications historically associated with medical epicondylectomy.

METHODS

A total of 27 subjects with clinical and electrodiagnostic evidence of cubital tunnel syndrome underwent a modified oblique medial epicondylectomy that was designed to minimize bony resection and preserve the origin of the ulnar collateral ligament of the elbow. Average age was 57 years, mean duration of symptoms was 24 months, and mean postoperative follow-up was 29 months. Eight patients had McGowan stage I disease, 14 had stage II, and 5 had stage III. Preoperatively, we measured intrinsic hand strength, 2-point discrimination, and residual medial elbow pain, and assessed for continuing signs and symptoms of nerve compression. Postoperatively, we added to the clinical examination elbow stability testing, elbow range of motion, and assessment of medial antebrachial cutaneous nerve injury. We collected patient-reported outcomes, including Quick Disabilities of the Shoulder, Arm, and Hand; Levine-Katz Severity Score; and Patient-Rated Elbow Evaluation.

RESULTS

We noted improvement of at least 1 McGowan grade in 20 of 27 patients (74%). Three of the 7 patients who had no change in McGowan grade still reported excellent patient-rated outcomes. Good to excellent results were achieved in 25 of 27 patients (93%). One patient had long-term severe medial elbow pain. Three patients had postoperative medial elbow pain that resolved with a single corticosteroid injection. One patient had a 30° flexion contracture; preoperative motion was not available for comparison. No patients had signs of elbow instability or numbness in the medial antebrachial cutaneous nerve distribution.

CONCLUSIONS

Modified oblique medial epicondylectomy was effective in improving symptoms in cubital tunnel syndrome. This medial collateral ligament sparing technique minimized complications previously associated with the original technique.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

The extraneural and intraneural arterial anatomy of the ulnar nerve at the elbow

The purpose of this report was to investigate the vascular anatomy of the ulnar nerve at the elbow with a technique of combined India ink and latex injection followed by nondissection chemical debridement. Twenty-two fresh human cadaveric arms were injected with India ink to stain the intraneural microcirculation followed immediately by latex injection and chemical debridement for study of the extraneural vascularization. After clearing with a modified Spalteholtz technique, the intraneural blood supply was studied in 10 of the specimens. The findings demonstrated a consistent but segmental extraneural and intraneural vascular supply from the superior ulnar collateral, inferior ulnar collateral, and posterior ulnar recurrent arteries. No identifiable direct anastomosis was seen between the superior ulnar collateral and posterior ulnar recurrent arteries in 20 of 22 arms. The inferior ulnar collateral artery provided the only direct vascularization to the nerve in the region just proximal to the cubital tunnel. Although the clinical importance of maintaining specific arterial sources to the ulnar nerve has not been determined, these anatomic findings indicate that the arterial contribution from the inferior ulnar collateral artery may be more important than appreciated previously.

The role of ulnar nerve transposition in ulnar nerve repair: a cadaver study

Ulnar nerve transposition at the elbow is recommended to diminish nerve gaps during neurorrhaphy. We undertook a cadaver study to determine the gap distance that can be overcome by subcutaneous transposition at the elbow, evaluating lacerations 2.0 cm distal to the medial epicondyle and 2.0 cm proximal to the wrist crease. With a 100-g load on each nerve stump, gaps that could be overcome were measured before and after transposition in different elbow and wrist positions. For the distal forearm lacerations, wrist position significantly affected nerve gap, while transposition and elbow position did not. Nerve gap was significantly reduced by approximately 11 mm with wrist flexion from 0 degrees to 45 degrees. For proximal forearm lacerations, gap distance was significantly affected by transposition and was dependent to a greater extent on the interaction between transposition and elbow position, with wrist position having no effect. A clinically relevant scenario for the proximal laceration compared the pretransposition gap with the elbow and wrist at neutral with the posttransposition gap with the elbow and wrist flexed. Posttransposition gap reduction, with elbow and wrist flexion at 45 degrees, was approximately 9 mm and was not significant. To span a gap near the elbow, we estimate that more than 45 degrees of elbow flexion is required.