Humeral Bone Loss in Revision Shoulder Arthroplasty
TAKE-HOME POINTS
- Different preoperative diagnoses lead to distinct patterns of bone loss in revision shoulder arthroplasty.
- A variety of techniques should be utilized to address the specific pathologies encountered.
- Advanced proximal humeral bone loss results in limited substrate available for humeral component fixation.
- Monoblock humeral stems can be used without allografts in cases with mild humeral bone loss.
- The revision of loose humeral stems dictates the use of large diaphyseal allografts in the majority of cases.
Management of the glenoid can have significant implications with regard to the humerus. Most notably, the size of the glenosphere has direct implications on the fixation of the humeral component. Use of larger diameter glenospheres result in increased contact area between the glenosphere and humerosocket, adding constraint to the articulation and further increasing the stresses at the implant-bone interface. As such, the use of larger glenospheres to prevent instability must be balanced with the resulting implications on humeral component fixation, especially in cases of severe bone loss.
After implanting the appropriate glenosphere, attention is then turned back to the humerus. Trial implants are sequentially used to obtain adequate humeral length and stability. Once this is accomplished, the amount of humeral bone loss is quantified by measuring the distance from the superior aspect of the medial humeral tray to the medial humeral shaft. If this number is >5 cm (Figure 3), the decision is made to proceed with an APC. The allograft humeral head is cut, cancellous bone is removed, and a step-cut is performed, with the medial portion of the allograft measuring the same length as that of bone loss and the lateral plate extending an additional several centimeters distally (Figure 4). Additional soft tissue is removed from the allograft, leaving the subscapularis stump intact for later repair with the patient’s native tissue. The allograft is secured to the patient’s proximal humerus using multiple cerclage wires, and the humeral stem is cemented into place. The final construct is shown in Figure 5.
ADDITIONAL CONSIDERATIONS: CASES OF ADVANCED BONE LOSS
In cases of advanced humeral bone loss, as is often seen when revising loose humeral stems, larger allografts that span a significant length of the diaphysis are often required. This type of bone loss has implications with regard to how the deltoid insertion is managed. Interestingly, even in situations when the vast majority of the remaining diaphysis consists of ectatic egg-shell bone, the deltoid tuberosity remains of fairly substantial quality due to the continued pull of the muscular insertion on this area. This fragment is isolated, carefully mobilized, and subsequently repaired back on top of the allograft using cables.
POSTOPERATIVE CARE
Patients are kept in a shoulder immobilizer for 6 weeks after surgery to facilitate allograft incorporation and subscapularis tendon healing. During this time, pendulum exercises are initiated. Active assisted range of motion (ROM) exercises begin after 6 weeks, consisting of supine forward elevation. A sling is given to be used in public. Light strengthening exercises begin at 3 months postoperatively.
DISCUSSION
In cases of mild to moderate proximal humeral bone loss, RSA using a long-stem humeral component without allograft augmentation is a viable option. Budge and colleagues38 demonstrated excellent results in a population of 15 patients with an average of 38 mm of proximal humeral bone loss without use of allografts. Interestingly, they noted 1 case of component fracture in a modular prosthesis and therefore concluded that monoblock humeral stems should be used in the absence of allograft augmentation.
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