Intraoperative Supraspinatus Strength, Histology and Correlation with the Outcome of Tendon Repair
Authors: DC Meyer et al.
References: Presented at AAOS 2004
Despite intact residual muscle functionality, following repair of chronic tendon tears muscle can hardly recover from fatty infiltration or artrophy.
Following tendon tear, the myotendinous unit suffers permanent retraction, atrophy and infiltration with fat. Reversal of these changes is known to be rare. To understand the functionality of such altered muscle tissue and the potential for recovery we stimulated the suprascapular nerve intraoperatively in thirteen patients during supraspinatus tendon repair and measured the maximal contractile muscle strength. Before and after repair, muscle biopsies were taken. The patients were assessed clinically and with MRI before and 3, 6 and 12 month after tendon repair.
Maximal contractile strength correlated strongly with the cross-sectional area and the fatty infiltration and ranged from 12 N/cm2 in Goutallier stage 3 to 42 N/cm2 in Goutallier stage 0. Of the five patients with re-tears, four were amongst the strongest six patients and one was the weakest of all. Muscle atrophy and fatty infiltration did not improve after successful tendon repair, but got significantly worse with recurrence of the tear. Histology revealed infiltration of fat and Lipofuszin in the muscles with marked atrophy and sings of disturbed muscle structure, predominantly in the biopsies taken after muscle stimulation.
We conclude that both, exceptionally strong or weak muscle conditions represent risk factors for recurrence of a tendon tear and need careful postoperative protection of the tendon repair. Maximal muscle contraction exceeded the strength of a single suture repair (200N), appears to cause further histological damage to already altered muscle tissue and should therefore be avoided. Atrophy and fatty infiltration seem irreversible, despite successful tendon repair.