Abstract and Introduction

Abstract

Although not reported to be common, rupture of the distal biceps tendon is an injury that results in a loss of supination and flexion strength. The injury is most commonly caused by eccentric load on a flexed elbow. At the time of injury, a noticeable "pop or tear" is usually experienced and a clinical deformity is often apparent. Current treatment for this injury is often anatomic surgical reattachment of the tendon to the radial tuberosity. This article is a brief review highlighting recent literature in the past year that adds to our understanding of treatment.

Introduction

Although not reported to be common, rupture of the distal biceps tendon is an injury that results in a loss of supination and flexion strength. The estimated incidence in the United States is 1.2–2.5 per 100,000 patients per year.^[1,2] The injury is most commonly seen in middle aged males and is often caused by eccentric load on a flexed elbow.^[1–4] At the time of injury, a noticeable "pop, snap, tear" is often felt or heard, and a clinical deformity known as the "reverse Popeye" often is readily apparent. Current treatment for this injury often is surgical reattachment; however, nonoperative management may be preferable for some patients. The following is a brief review highlighting recent literature in the past year that adds to our understanding of methods of treatment and pathophysiology of this injury.

Diagnosis

History and examination often are adequate to make a diagnosis; however, MRI can be very helpful for confirmation of unclear cases. Partial tears, isolated bundle tears, and complete tears in which the tendon is caught in the lacertus fibrosus may obscure clinical deformity. MRI with flexed elbow, abducted shoulder, forearm supinated (FABS) positioning has been shown to be particularly helpful in the diagnosis of partial or isolated bundle tears.^[5]

Anatomy

A better understanding of the anatomy around the distal biceps tendon has led to advances in treatment and understanding the pathophysiology of tears. The biceps tendon is composed of two heads and is innervated by the musculocutaneous nerve. The long head of the biceps tendon originates from the supraglenoid tubercle, while the short head originates from the coracoid process and merges with the long head at the level of the deltoid tuberosity. Distally, the long and short head tendon units maintain distinct functional insertions; the long head inserts onto the bicipital tuberosity more proximally and contributes a greater supination moment while the short head inserts more distally and anteriorly generating a greater flexion moment.^[6] The lacertus fibrosus originates at the level of the musculotendinous junction and consists of three distinct layers, enveloping the forearm flexor muscles and serving as a stabilizer to the distal tendon.^[7]

The vascularity of the distal portion of the tendon has proximal, middle, and distal zones.^[8] The proximal zone encompasses the musculotendinous junction and proximal tendon where branches of the brachial artery extend across and continue within the tendon paratenon. Branches originating from the posterior interosseous recurrent artery supply the distal zone at the biceps tendon.^[8] The middle zone is a hypovascular zone, averaging 2.14 cm in length, which is supplied by branches from both of these major arteries but only through a thinner paratenon covering.^[8] Seiler et al.^[8] hypothesized that the relatively limited vascular supply of the middle zone may contribute to a diminished ability to support tendon repair, and the zone may be prone to secondary rupture and injury.

The lateral antebrachial cutaneous nerve (LABCN) is a terminal branch of the musculocutaneous nerve and has been shown to consistently emerge near the lateral aspect of the distal biceps tendon, usually traveling with the cephalic vein. This nerve bifurcates into a volar branch, supplying the lateral volar portion of the wrist skin and portions of the thumb, and a dorsal branch, supplying the distal two-thirds of the dorsolateral forearm skin. The posterior interosseous nerve (PIN) is the continuation of the deep branch of the radial nerve and supplies motor-to-hand and wrist extensors. It is at risk during exposure, retracting, and drilling. Hackl et al.^[9] described how the PIN courses 10 mm proximal to the bicipital tuberosity in supination and 5 mm distal to it in pronation during the anterior approach.

The radial recurrent artery branched from the radial artery lies superficial to biceps and is encountered with anterior exposure of the distal biceps. Zeltser and Strauch^[10] have described variations of the radial recurrent artery at the level of the radial tuberosity. The anatomical study showed one can expect most often to find a single radial recurrent artery with two branches located between 19 mm proximal and 4 mm distal to the proximal aspect of the tuberosity. The radial recurrent artery will be at least 9 mm superficial to the tuberosity. In addition to arterial structures, two to four deep venous structures traverse the field along with the radial recurrent artery. Therefore, during a typical anterior approach to the distal biceps, three to six deep vascular structures may require cauterization or ligation. In addition, during a typical anterior repair the tendon stump is brought down to the tuberosity along a path that should remain dorsal to any recurrent arteries. The study showed that about half the time, there might be a recurrent artery dorsal to the path of the tendon.

Pathophysiology

Seiler et al.^[8] showed a potential anatomic and vascular reason for failure. They showed a relative hypovascular zone 2.14 cm in length at the mid distal portion of the tendon and a 50% dynamic narrowing for the tendon passage between the lateral ulnar border and the radial tuberosity as the forearm rotates into pronation. The relative hypovascularity combined with mechanical impingement might explain the reason for tendon rupture at its distal insertion.^[8]

Function

Morrey et al.^[11] were among the first authors to report that the loss of the distal biceps attachment could result in a 40% loss of supination strength, 79% loss of supination endurance, 30% loss of flexion strength, and 30% loss of flexion endurance. More recently, Neterenko et al.^[12]showed significant reductions in peak flexion and supination torque but no significant difference in fatigue in nine patients with distal biceps tears. Schmidt et al.^[13]showed a 60% reduction of supination strength in 23 patients with unrepaired distal biceps ruptures. Jarrett et al.^[6] examined the short head and long head of the distal biceps as discreet functional units. They showed that the long head inserts more proximal and has a greater supination moment, while the short head insertion is more distal and generates a greater flexion moment.

Studies often measure improvement against the contralateral arm. More recently, Kerschbaum et al.^[14]explored differences of elbow flexion and supination strength between the dominant and nondominant arm to improve understanding of outcome studies measuring strength differences after repair. They found that differences in biceps strength depended on sex, handedness, and regular practice of overhead sports. They recommended that when compared to the contralateral side some adjustments need to be made; in general, supination strength tends to be 7% higher on the dominant side and flexion strength often is equivalent.

Treatment

Operative Treatment

Description of a distal biceps tear seems to have appeared as early as 1843 by Stark and a report of fixation in 1898.^[15]Surgical repair in many early case series was associated with a high rate of radial nerve palsies, and for many years nonoperative treatment or tenodesis to the brachialis was often recommended. In 1961 Boyd and Anderson published a two-incision technique that provided exposure to the radial tuberosity for direct repair and attempted to limit radial nerve injuries seen with the previous all-anterior surgical approaches.^[16] The success of the two-incision technique and two subsequent reports published in 1985 of improved outcomes with operative treatment versus nonoperative treatment by Baker and Bierwagen^[3] and Morrey et al.^[11] advanced the indications for operative treatment. Later, advances in anchor technology and an attempt to limit cases of synostosis led to a resurgence of the anterior approach.

Two techniques are primarily now used. The single anterior incision approach secures the distal biceps tendon with either suture anchors or a cortical button and a two-incision posterior approach that secures the distal biceps tendon through bone tunnels, anchors, or an intraosseous button. Both approaches have been extensively studied and show favorable clinical outcomes regarding patient-reported outcomes and objective return of supination and flexion strength compared to nonoperative treatment.

Endoscopic-assisted Repair

Endoscopic repair techniques have been described recently.^[17,18] These techniques have been typically utilized for evaluation and treatment of partial tears and acute tears. Bhatia et al.^[19] has reported an endoscopic technique for treating acute and chronic retracted tears. By using three separate portals that have been previously described,^[20] they were able to repair a chronically retracted biceps tear. Although technically feasible, the author cautions on the difficulty of the procedure and recommends cadaver experience.

Comparisons Between Approaches

Recent meta-analyses and systematic reviews in the past few years have shown differences in complication rates between the anterior and posterior approaches. Often these have shown a trend toward a lower complication rate of the posterior approach, which is a reversal of trends seen previously.^[21–23] In light of these observed trends a recent study published by Waterman et al.^[20] performed a retrospective comparative study looking at the results of military patients treated for primary distal biceps ruptures between 2007 and 2013. Two hundred and fourteen patients were treated with an anterior approach and 70 patients with a posterior approach. After regression analysis and comparative analysis, no significant differences were identified. The most frequent complication in both groups was that of transient LABCN neurapraxia. This was higher in the anterior approach than with the posterior approach, but the consequence of this complication did not affect final clinical analysis in either group, with 97% returning to full preoperative function.

Differences in Arm Strength after Single-incision versus Two-incision Approach

Although improved through anterior or posterior (two-incision) surgical reattachment, objective strength is affected by technique according to Schmidt et al.^[24] They found that a posterior approach was in general associated with improved supination strength compared to the anterior approach at 60 degrees of supination. Interestingly, supinator fat infiltration after a posterior approach negatively affected the results of strength that was achieved by this more anatomic insertion. Despite these differences, Disability of the Arm, Shoulder, and Hand (DASH) scores did not show a difference between the two groups.

Isolated Repair of Short Head of the Biceps

Although some anatomic variation of insertion does exist,^[6,7,25,26] it appears that the discrete short-head and long-head insertions play individual roles in effecting supination and flexion at different levels of elbow angulation and rotation.^[6] As these different roles have been recognized, addressing isolated bundle tears has gained more attention. In the last several years a few case reports have described repair of isolated bundle tears with good results.^[5] Voleti et al.^[5] reviewed three isolated short-head ruptures. All three patients underwent MRI for confirmation of injury and had successful repairs. They discussed some challenges in identifying short-head ruptures from a partial tear of a common tendon and highlighting the potential to provide good outcomes with isolated or concomitant repair.^[5]

Delayed Repair

Distal biceps tears are not always promptly recognized or the impairment is not immediately appreciated, and consequently the patient presents in a delayed fashion. Some have reported significantly increased complications for patients undergoing a delayed repair as compared to acute repairs. Kelly et al.^[27] showed that the complication rate increased from 24% to 41%. Bisson et al.^[28] reported the complication rate increased from 20% to 40%. Cain et al.^[29] reported that the complication rate increased from 30% to 46%. A study by Haverstock et al.^[30] reported the outcomes of delayed repairs compared to a cohort of acute repairs. Similar to previous studies they found an increase in the complication rate when compared to acute repairs 63% versus 29%. The most common complication was transient LABCN neurapraxia (8/10). DASH, Patient-Rated Elbow Evaluation (PREE), American Shoulder and Elbow Surgeon (ASES) scores showed no statistical difference. Isometric supination and flexion strength showed no statistical difference. Delayed repair seems to offer comparable functional results as acute repair, but patients should be counseled about the increased complication rate.

Nonoperative Treatment

Not all patients can or do elect to undergo reattachment surgery, and a few studies recently have sought to understand differences in the expected outcomes without surgery. Freeman et al.^[31] retrospectively reviewed 18 patients treated nonoperatively and found a consistent reduction of supination strength (63% of contralateral) and flexion strength (93% of contralateral). The mean DASH score was 14, which is close to the mean DASH score for normal adults 10.1±14.7.^[31] Legg et al.^[32] evaluated supination and flexion strength 6 mo after Endobutton (Smith and Nephew, Andover, MA) repair of the distal biceps injury and compared those results to a cohort of nonoperatively managed patients at least 6 mo after injury (average follow-up 3.3 yr). The nonoperatively managed patients showed 70% flexion strength and 59% supination strength compared with the uninjured arm. In contrast, patients with the Endobutton repair showed elbow flexion strength of 92% and supination of 87% compared to the uninjured arm. The mean QuickDASH score for the operatively treated group was significantly better than the nonoperative cohort 6.29 versus 14.10.

Rehabilitation

With biomechanical evidence supporting good initial repair strength, some protocols have advocated for immediate range of motion, while traditional protocols have often started range of motion 1–2 wk after surgery.^[33–35] Smith et al.^[36] retrospectively reviewed their outcomes when allowing immediate range motion after an anterior repair using a cortical button. They saw no evidence of tendon rupture or failure, wound problems, or patient dissatisfaction.

Complications

Recent estimates of the overall complication rate with surgical repair have been 22% to 24.5%.^[22,37] The most commonly reported complications are transient LABC neurapraxia, superficial wound infections, heterotopic ossification, synostosis, posterior interosseous nerve palsy, and rerupture.^[21,22] The risk of LABC injury is typically associated with an anterior approach.^[21,22]

Preventing Synostosis. Heterotopic ossification resulting in synostosis can be a debilitating complication after distal biceps tendon repairs. Most commonly it has been reported with two-incision techniques but it is also recognized with anterior approaches as well.^{[24,27,38,39]}Costopoulos et al.^[40] retrospectively reviewed 112 patients surgically treated for distal biceps tears with modified Boyd-Anderson technique (105) or anterior approach (seven). One hundred and four patients received indomethacin, from 10 to 42 days as prophylaxis for heterotopic ossification. Only one of the patients on indomethacin developed a synostosis as compared to three without prophylaxis. Importantly, no evidence of delayed healing, side effects, or functional complications were noted with indomethacin use. They believe it is reasonable to consider indomethacin as synostosis prophylaxis.

Failure of Repair. Recent estimates of re-rupture have been 1.5% to 1.6%.^[22,41] Mechanical impingement may play a role in recurrent injury or failure of repair. Krueger et al.^[42] showed how surgical fixation technique may lead to posterior impingement of the tendon at the repair site due to the same anatomic constriction between the ulna and radius. Bhatia et al.^[7] evaluated potential impingement of the tendon between the radial tuberosity and ulna after simulated repair. The anatomical study showed as others that the radial ulnar space (RUS) allowing for clear passage of the tendon during rotation decreases significantly from pronation to supination. By precisely measuring across different degrees of rotation they also showed that an increase in thickness as little as 2–3 mm of the repaired tendon from the native tendon could lead to impingement. They also measured the length of the footprint and evaluated potential impingement along three zones (proximal, middle, and distal), finding that the more distal portion of the tuberosity has a narrower RUS than the more proximal portion. Other notable findings were: defining three subtypes of footprint anatomy related to the variation of short-head and long-head insertions; showing mean tuberosity dimensions of length of 23.8 mm, width of 13.4 mm, and thickness of 16.3 mm. They postulated that techniques that can avoid increasing the thickness of the repaired tendon and using a reattachment site more proximal along the tuberosity could avoid mechanical impingement after repair.

Tendon Elongation. Most recent constructs for tendon fixation have shown sufficient strength to allow early passive and active range of motion, which has been incorporated into many surgeons' postoperative therapy protocols.^[33,43–45] However, discussion of potential tendon elongation or creep after distal biceps repair with these protocols has been limited. Marshall et al.^[46]evaluated 11 patients with distal biceps ruptures (10 complete ruptures and one partial). Surgical fixation was performed via an anterior approach with a cortical button (Smith & Nephew, Andover, MA) and No. 2 FiberWire (Arthrex, Naples, FL). During repair, two 2-mm tantalum beads with laser-etched holes were sutured to the distal biceps tendon. Using radiographs they evaluated the position of the beads at time 0 and then at 4, 8, and 16 wk postoperatively.

Postoperative protocols were standardized for all patients. Patients were placed into a posterior mold splint at 90 degrees of flexion, which was removed at the first postoperative visit 7 to 10 days postoperatively. After splint removal, patients were instructed to begin passive elbow range of motion and began physical therapy. Passive range of motion was limited to 30 to 120 of flexion. Passive supination and pronation were also allowed but not performed near full extension. Active supination as well as elbow flexion and extension were allowed at 3 wk with no resistance and a goal of full extension at 6 wk. Resistance exercises began at 6 wk, with gradual increase in strengthening. Full return to vigorous labor or sports was allowed after 4 mo, which was after the final follow-up visit for the study.

They found mean tendon lengthening after surgery was 22.8 mm (range, 11.2–30.9 mm; P<0.05), and the repair site lengthened a mean 17.0 mm (range, 9.6–30.6 mm; P<0.05) from surgery to final follow-up. The greatest change in lengthening was noted between time 0 and week 4 (mean, 11.3 mm; P<0.05), with the least amount of lengthening between weeks 8 and 16 (mean, 2.6 mm; P<0.05). The mean DASH score was 11.2. Final ultrasound evaluations found all tendons to be in continuity. If further study of this observation shows that elongation has an inverse relation to functional improvement, we could expect alterations to rehabilitation protocols or fixation techniques in the near future.

Conclusion

Distal biceps tendon injuries continue to be an area of clinical focus. New research has reinforced the understanding that injury to the distal biceps tendon results in strength impairment and that techniques of repair have implications of how much strength will be restored. Operative treatment is typically recommended for most patients with higher activity levels and continues to show functional advantages compared to nonoperative treatment. Single-incision repairs and two-incision repairs both show excellent clinical outcomes, but awareness of complications associated with each technique is essential.