Is failure of tuberosity suture repair in hemi-arthroplasty for fracture mechanical?

BackgroundTuberosity suture repair in hemiarthroplasty for fracture carries risk of malunion giving poor results. Is failure mechanical or biochemical? We investigated the mechanical aspect with repetitive loading in cadaveric repairs.Materials and methodsTests were carried out in line with U.K. Human Tissue Authority regulations. A 4-part fracture was created in 8 cadaver shoulders by osteotomizing the tuberosities. A standard hemiarthroplasty implant was cemented in at correct height and retroversion, and standardized repairs applied. Initial firmness of repair was confirmed by attempting to manually displace the tuberosities with a forceps in multiple planes. All pre-stress tests showed 0 mm movement. Repairs were then subjected to cyclical tension on the cuff musculature and simultaneous gleno-humeral motion for 8000 cycles. The tuberosities were reprobed with a forceps to record any movement.ResultsDefining repair failure as the ability to manually displace a tuberosity more than 3 mm, every specimen failed: 100% failure (exact 95% confidence interval 65.2-100% due to sample size). Movements of at least 1 cm were commonly observed. The sutures were loose but had never snapped. Sutures were noted to dig into the tendon and cut partially through bone. Collapse of cancellous bony volume led to looseness and migration of the sutures.ConclusionSuture repair of tuberosities has mechanical weaknesses; failure may be a mechanical phenomenon.