| Year : 2007 | Volume : 1 | Issue : 1 | Page : 16-22 |    |
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Subscapularis dysfunction after open instability repair has recently received increasing attention. Various clinical studies indicate that surgical approaches using partial or complete subscapularis tendon takedown techniques might impair subscapularis recovery and can negatively influence the final clinical outcome. This review article will focus on the potential pathogenesis, diagnosis, and clinical impact of the unrecognized condition and summarizes the currently available literature.
Keywords: Open instability repair, shoulder instability, subscapularis dysfunction
| How to cite this article: Scheibel M. Subscapularis dysfunction after open instability repair. Int J Shoulder Surg 2007;1:16-22 |
Open shoulder stabilization procedures have been considered the gold standard for recurrent anterior shoulder instability with success rates in the recently published literature ranging from 86.6 to 97%.[1],[2],[3],[4],[5] With the advancement and success of arthroscopic techniques compared to the results of open repairs there is currently a growing trend toward arthroscopic treatment of shoulder instabilities.[6],[7] However, open stabilization procedures retain their indications in the setting of anterior instability with large bony defects and/or soft-tissue deficiencies and in cases where the surgeon lacks the experience and surgical skills to perform the repair arthroscopically.[8] Open stabilization requires different types of subscapularis (SSC) tendon take-down (complete SSC tenotomy approach/inverted L-shaped SSC tenotomy) or incision techniques (SSC split approach) [Figure – 1],[Figure – 2],[Figure – 3]. Despite previous belief that open instability repair might not significantly disturb the integrity of the SSC musculotendinous unit post-operatively, SSC dysfunction has recently received increasing attention and appears to occur more frequently than previously appreciated.[9],[10],[11],[12],[13],[14]
Post-operative insufficiency of the SSC unit might occur due to different reasons including failure of the tendon repair and/or muscular changes (atrophy and fatty infiltration) resulting in loss of SSC function. The incidence of failed tendon repairs after open shoulder stabilization has not been clearly investigated. In a retrospective study, Greis et al . reported on 88 patients who underwent an open Bankart procedure using a complete SSC tenotomy approach.[9] Of these, four patients (4.5%) required re-operation due to SSC tendon repair failure. However, other series did not report any revisions due to post-operative SSC tendon disruption.[1],[3],[5],[6] Maynou et al . found three cases (3.9%) of failed repairs in a group of 77 patients who underwent the Latarjet-procedure using the inverted L-shaped tenotomy approach and were followed-up with Arthro-CT.[10] Two of the three patients had marked fatty infiltration (stage 3 and 4 according to Goutallier), however, re-operation was not required. Apparently such tears are not always recognized when patients presented post-operatively. A failed repair that remains undetected seems to follow the natural history of a traumatic SSC tendon rupture including scarring and progressive atrophy and fatty infiltration making the musculotendinous unit irreparable. Proposed factors associated with postoperative SSC rupture have included multiple operations with poor tissue quality, trauma, inappropriate physical therapy and insufficient repair techniques.[14],[15],[16]
Atrophy and fatty infiltration of the SSC muscle in cases of an intact repair have also been noted and the reason for the degeneration of the muscle has not been finally investigated.[14],[15] Miller et al . suggested the possibility of denervation during the surgical approach with release and mobilization of the SSC musculotendinous unit.[16] The SSC receives its innervating fibers from SSC nerves (mainly superior, middle, and inferior branches) that arise in the majority from the posterior cord of the brachial plexus or in rare cases directly from the axillary nerve penetrating the muscle belly at its anterior aspect.[17],[18],[19] Mobilization including the release of adhesions at the upper border, at the anterior surface between the conjoined tendons and the muscle and along the scapular neck at the posterior surface of the SSC musculotendinous unit places the integrity and innervation of the muscle at risk. Different cadaveric studies have attempted to provide surgical guidelines for safe surgery about the SSC muscle. Yung et al . considered the anterior surface of the SSC muscle underneath the conjoint tendon as a “safe harbor.”[19] Checcia et al. evaluated the topographic relationship of the penetrating nerves to anterior rim of the glenoid concavity according to the position of the arm and found that the upper SSC nerve branch penetrates the muscle as close as 1cm from the medial border of the glenoid.[17] All the investigated nerve branches were closest to the anterior border of the glenoid when the arm was changed from internal to external rotation. In a recently presented paper it has been shown that all superior SSC nerve branches were located within a range 2.5 cm vertical distance below the base of the coracoid process.[18] Within this vertical distance there was a 95% probability to find upper SSC nerves beyond a 2 cm distance medially from the lateral border of the coracoid base with the arm in neutral rotation. After circumferential release and with lateral traction on the tendon there was a 95% chance to find nerve branches 0.5 cm medially from the lateral border of the coracoid base. It seems that there is an increased risk for denervation in particular of the upper part of the SSC muscle when the release is performed anterior to the muscle beyond the coracoid base in particular with a lateral pull on the tendon. These anatomical data are in accordance with clinical and radiological findings that in particular the upper SSC muscle portion shows clinical dysfunction and structural changes.[13],[14] Electromyography and nerve conduction studies may further add in clarifying the pathogenesis.
The SSC muscle represents an integral part for optimal shoulder function. It acts as an important internal rotator, shoulder abductor and abductor depending on the humeral head position, and active anterior stabilizer of the glenohumeral joint.[20],[21],[22],[23],[24] In addition the SSC represents the anterior part of the transverse force couple and therefore balances the external rotators of the shoulder.[25] Cadaveric, biomechanical, and electromyographic studies demonstrate the SSC muscle to have at least two different innervations and major functions.[17],[18],[26],[27],[28],[29] Liu et al . suggested that the superior portions may play an important role in generating abduction torque and the inferior portions may enhance stability.[30] According to this data post-operative SSC dysfunction may therefore affect and influence the final clinical outcome after open instability repair.
History and physical examinations are helpful in establishing the diagnosis. The physician should be suspicious of a failed tendon repair in patients who underwent prior open instability repair and present with recurrent instability, weakness in internal rotation and increased passive external rotation in the early postoperative period.[9] However, as mentioned above, it seems that often such tears remain undetected unless a meticulous physical examination is performed. In the early postoperative period the specific clinical testing interferes with the healing of the tendor. The clinical diagnosis of SSC dysfunction is based on the currently available diagnostic tests and clinical signs that have been published to detect SSC tendon tears. The lift-off test as described by Gerber and Krushell is considered positive if the patient is unable to raise the arm posteriorly off the back[31] [Figure – 4]. If the lift-off test is per definition negative, the greatest distance hand to back achieved actively during the lift-off test can be measured and compared to the opposite side. This measurement allows specifying the test result. The internal rotation lag sign as described by Hertel et al. is considered as positive if the patient cannot actively maintain the position of internal rotation and extension [Figure – 5],[Figure – 6].[32] With the belly-press test the patient presses the abdomen with the hand flat and attempts to keep the arm in maximum internal rotation. The test is considered positive when the elbow drops in a posterior direction, internal rotation is lost and pressure is exerted by extension of the shoulder and flexion of the wrist.[33] We perform this test in a slightly modified manner. With the hand flat on the abdomen and the elbow close to the body the patient is told to bring the elbow forward and straighten the wrist. If the patient cannot achieve full extension the final flexion position of the wrist is measured as described by Burkhart and Tehrany for the Napoleon sign or Kim et al . for the belly-press test (belly-press angle) using a hand-held goniometer[34],[35] [Figure – 7],[Figure – 8]. In a recently published study we were able to show that the belly-press angle correlated with the degree of structural changes of the SSC muscle after open shoulder instability repair meaning that higher values had a higher degree of fatty infiltration of the SSC muscle. We could also show that the belly press test and the belly off sign, defined as the inability of the patient to maintain the palm of the hand attached to the abdomen with the arm passively brought into flexion and internal rotation, were the most reliable signs to detect mild upper SSC dysfunction[13],[14],[36] [Figure – 9],[Figure – 10]. It seems that the lift-off test becomes only positive if marked structural changes (tendon failure and/or marked fatty infiltration) are present.
Different imaging methods have been described to evaluate the SSC musculotendinous unit postoperatively. Although a certain amount of experience is necessary, ultrasound represents a useful tool to monitor SSC tendon integrity in the immediate post-operative period since it is cheap and easy to perform.[37] In addition the clinical evaluation using the above described tests interferes in the early post-operative period with the process of tendon healing. Different authors used Arthro-CT to detect tendon tears and grade the fatty infiltration according to Goutallier et al .[10],[11],[38] We recently used magnetic resonance imaging to evaluate the structural integrity of the SSC musculotendinous unit. Criteria for detection of SSC tendon tears on axial images are fluid equivalent signal in the way of a tendon, discontinuity, or retraction of the tendon. Circumscribed signal alteration of the tendon or caliber changes as described by Pfirrmann et al . cannot be used as diagnostic criteria since previous surgery had been performed.[39] MRI can also be used to evaluate atrophy and fatty infiltration of the SSC muscle[13],[14] [Figure – 11].
The clinical impact of postoperative SSC dysfunction is currently a matter of debate. Acute postoperative tendon disruption due to a traumatic event may lead to recurrent instability, weakness in internal rotation and increased passive external rotation in the early post-operative period. In the study by Greis et al . a prompt re-exploration and repair of the SSC tendon was performed to achieve adequate stability and SSC function. The authors recommended strong
re-fixation technique, a supervised post-operative treatment protocol, and the use of less invasive exposure techniques. Unless the failed repair is detected and reconstructed promptly the SSC musculotendinous unit often retracts and undergoes atrophy and fatty infiltration. When the SSC tendon is deficient or irreparable a pectoralis major transfer may be used to augment or substitute the SSC musculotendious unit.
In contrast to acute postoperative tendon disruption, chronic SSC insufficiency appears to be a different problem. In a retrospective study Picard et al . evaluated the effects of subtotal vertical section (inverted L-shaped SSC tenotomy) of the SSC tendon in 40 patients who underwent open shoulder stabilization using the Latarjet procedure.[11] The SSC muscle was assessed by measuring strength for internal rotation and the distance hand to back during the lift-off test. The structure of the SSC muscle was assessed by CT scan. Four years after the surgical procedure the authors found a 50% loss of the SSC muscle strength and significant fatty degeneration of the muscle (stages II-IV according to Goutallier) in 41% of patients. The authors therefore recommended to avoid this approach for the Latarjet procedure.
In a subsequent study, Maynou et al . compared the clinical function and structure of the SSC muscle after Latarjet-Patte procedure using an inverted L-shaped tenotomy approach vs. a lengthwise incision (SSC-split).[10] The SSC function was evaluated measuring distance and strength by the lift-off test. Integrity of the tendon and fatty degeneration and atrophy of the muscle were also analyzed by Arthro-CT. The authors found that the distance and strength were significantly reduced and fatty degeneration was significantly increased in the inverted L-shaped tenotomy group. In addition three partial tendon disruptions had been observed. According to the Walch-Duplay score patients in this group had less satisfying overall clinical results. The authors concluded that the inverted L-shaped tenotomy results in loss of strength, fatty degeneration and atrophy of the muscle belly and recommended the SSC split as the standard approach for the Latarjet-Patte procedure.
Sachs et al . recently looked at thirty patients after primary open Bankart-repair using an L-inverted tenotomy approach.[12] The authors analyzed their results according to SSC function. Twenty-three patients (77%) were thought to have a competent SSC (negative lift-off test) and seven patients (23%) were thought to have an incompetent SSC demonstrated by a positive lift-off test. No difference was found between both groups using the Constant score and the American Shoulder and Elbow Surgeons scoring system (ASES). However, patients with a competent SSC had higher subjective satisfaction rates and higher values in the Western Ontario Shoulder Instability Index (WOSI). In fact the lower WOSI scores confirmed that the SSC dysfunction correlated with an inferior subjective outcome. Because only one of the patients with SSC dysfunction had a postoperative MRI it was impossible to establish a correlation between the clinical deficit and post-operative structural changes of the SSC musculotendinous unit.
In a recently published study we evaluated the integrity, structure, and clinical function of the SSC musculotendinous unit in patients after primary and revision open shoulder stabilization using an inverted L-shaped tenotomy approach and compared the results with the overall function of the shoulder.[14] Although no complete tendon disruption was found, we were able to demonstrate that an inverted L-shaped SSC tenotomy approach may lead to atrophy and fatty infiltration in particular of the upper part of the SSC muscle. Revision procedures using the same approach did significantly further compromise clinical SSC function and structural integrity. Although we did not find any statistically significant differences in the Constant-Scores and Rowe-Scores between both groups, the modified belly-press test/Napoleon sign and the belly-off sign appeared to be the most reliable signs to detect upper SSC dysfunction.[14],[36]
The results of the above mentioned studies suggest that with regards to the deterioration of the clinical function and structure of the SSC muscle a SSC split or even an arthroscopic approach may potentially less violate the musculotendinous unit. In a so far unpublished study, we evaluated the integrity, structure, and clinical function of the SSC musculotendinous unit after arthroscopic and open shoulder stabilization using a complete SSC tenotomy approach.[40] We were able to confirm previous observations that open shoulder stabilization using a SSC tenotomy may lead to atrophy and fatty infiltration in particular of the upper SSC muscle portion resulting in post-operative SSC dysfunction. As expected, arthroscopic procedures using a three portal technique did not significantly compromise clinical SSC function and structural integrity. However no significant differences were observed in the overall outcome.
In summary, open shoulder stabilization procedures bear the risk of iatrogenic damage to the SSC musculotendinous unit. Irreversible changes of the muscle, in particular atrophy and fatty infiltration with or without failure of the tendon repair, may result in loss of SSC function. It seems that in cases of a successful capsulolabral repair a moderate to severe SSC dysfunction needs to be present before the results of functional shoulder scores become significantly affected. The SSC split approach seems to be the most benign approach for the open instability repairs with regards to SSC integrity. However if partial or complete tendon detachment and mobilization techniques are performed the procedure should be carried out with respect to the neural innervation of the SSC muscle. Strong tendon repair techniques should be used and the repaired tendon must be protected postoperatively. Arthroscopic techniques do not seem to significantly influence SSC function and integrity and should therefore be used if indicated.
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Figures
[Figure – 1], [Figure – 2], [Figure – 3], [Figure – 4], [Figure – 5], [Figure – 6], [Figure – 7], [Figure – 8], [Figure – 9], [Figure – 10], [Figure – 11], [Figure – 12]
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