Infraspinatus and Deltoid Length and Patient Height: Implications for Lateralization and Distalization in Reverse Total Shoulder Arthroplasty
Peter N. Chalmers, MD, Assistant Professor,a,* Spencer R. Lindsay, MPA, Research Associate,b Weston Smith, BA, Research Associate,b Jun Kawakami, MD PhD, Research Associate,b Ryan Hill, MD, Orthopaedic Resident,c Robert Z. Tashjian, MD, Professor,d and Jay D. Keener, MD, ProfessoreShoulder
Background:
Restoration of muscular strength is predicated on restoration of muscle length. The purpose of this study was to describe infraspinatus and deltoid length preoperative to reverse total shoulder arthroplasty (RTSA) to guide distalization and lateralization to restore preoperative muscle length.
Methods:
This was a retrospective radiographic study. On preoperative computed tomographic imaging we measured infraspinatus length. On preoperative x-ray we measured deltoid length. For all measurements, reliability was first established by comparing measurements between two observers and intra-class correlation coefficients (ICCs) were calculated. We then calculated descriptive statistics for these muscular lengths and developed a formula to predict these muscular lengths from patient demographics.
Results:
We measured infraspinatus length in 97 patients and deltoid length in 108 patients. Inter-rater reliability was excellent, with all ICCs >0.886. Mean±standard deviation infraspinatus length was 15.5±1.3 cm but ranged from 12.6 to 18.9 cm, while deltoid length was 16.2±1.7 cm but ranged from 12.5 to 20.2 cm. Both infraspinatus (r=0.775, p<0.001) and deltoid length (r=0.717, p<0.001) were highly correlated with patient height but did not differ between diagnoses. Formulae developed through linear regression allowed prediction of muscle length to within 1 cm in 78% and within 2 cm in 100% for the infraspinatus and 60% and 88% for the deltoid.
Conclusion:
Deltoid and infraspinatus length are variable but highly correlated with patient height. To maintain tension, two mm of lateralization and distalization should be added for every 6 inches (~15 cm) of height above average for a Grammont-style RTSA.
Level of Evidence:
Anatomy Study; Imaging
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