Surface Replacement Arthroplasty of the Shoulder
The results of the Mark 2 design were published in 2001 . 103 shoulders were implanted into 94 patients (9 bilateral). There were 73 females and 21 males. The mean age at the time of surgery was 64.3 years (Range 22-88y). Total shoulder replacement (TSR) was used in 68 cases and Hemiarthroplasty in 35. The average length of follow-up was 6.8 years (Range 5 years to 10 years).
1. Constant Scores
The pre-operative average Constant Score was 15.4 points or 24% after adjustments for age and gender. Post-operative Constant Scores at follow-up was 52.4 points or 75.2% after adjustments for age and gender. Best results were achieved in cases of primary Osteoarthritis with Constant scores of 93.7% for TSR and 73.5% for Hemiarthroplasty. The poorest results were encountered in patients with cuff arthropathy, Instability arthropathy and other causes (arthropathy post septic arthritis) with adjusted Constant Scores of 61.3%, 62.7% and 58.7% respectively. Active elevation improved by an average of 69 degrees to an average of 133 degrees for Osteoarthritis and avascular necrosis and to an average of 105 degrees for Rheumatoid Arthritis. For Instability arthropathy and Cuff arthropathy this increased to an average of 97 degrees and 73 degrees, respectively. Pre-operative and post-operative differences were statistically significant for all the disease groups (p<0.001).
2. Patients subjective assessment
93.9% reported that their shoulder was much better or better. 6.1% of patients were disappointed and considered themselves to be the same as before surgery, usually because of limited range of motion but they were satisfied with pain relief .
3. Radiological results
There was a 5.1% incidence of progressive lucent lines of more than 2mm, with signs of definite loosening. Since using the hydroxyapatite-coated implants, no lucent lines have been observed. The relevance of the radiolucent line is uncertain, but seems unrelated to the outcome.
In 5 shoulders some degree of mild humeral prosthesis subsidence was found. There seemed to be no effect of the mild subsidence on the clinical result.
1. Myositis Ossificans - 0.7%
2. Aseptic loosening - 5.1%
3. Periprosthetic fracture - 0.7%
4. Superficial Infection - 1.4%
5. Deep Infection - 0.7%
5. Revision surgery
The revision rate at five to ten years of using the Mark 2 design has been 6%. The indications were:
1. Instability following total shoulder resurfacing arthroplasty for instability arthropathy in two patients.
2. One periprosthetic fracture following a fall
3. One disassociation of the polyethylene glenoid from the metal part of the glenoid component
4. One glenoid loosening following a fall
5. Two aseptic loosening - One involved both humerus and glenoid, and one glenoid only.
Removal of the humeral surface component was easily and speedily done as no cement or prosthetic stem had to be exposed and removed. Removal of cemented stemmed prosthesis is associated with loss of bone stock, perforation and fracture of the humeral shaft.