Introduction

Shoulder pathology is a common source of pain and disability affecting patients with a prevalence of 17% [1]. Shoulder replacement can provide satisfactory results through restoration of shoulder congruity that improves range of motion and decreases pain sensation [2].

The optimal surgical treatment for glenohumeral osteoarthritis with an intact rotator cuff is still under debate [3–5]. Good outcomes of total shoulder arthroplasty have been shown to last for an average of at least 10 years. Glenoid component loosening in up to 39% remains the most frequent indication for revision surgery [6–12].

Resurfacing shoulder replacement of the proximal humerus is a viable alternative to conventional shoulder replacement to restore shoulder function in patients with osteoarthritis. The first surface replacement was designed by Copeland and was performed only in young and active patients in the mid 1980s [13, 14]. After this initial period, surface replacement has been popularized and increasingly used in elderly patients and has also been described as a viable treatment option for many indications, such as osteoarthritis, avascular necrosis, rheumatoid arthritis, rotator cuff tear and post-traumatic arthritis [6, 15–22]. Some of the advantages are the preservation of the humeral bone stock which eases the conversion to a stemmed total or reverse shoulder prosthesis if a revision becomes necessary [13, 19, 22, 23]. Other potential benefits include the shorter operation time, less risk of periprosthetic fractures and less per-operative blood loss. Studies report satisfactory results at short- and mid-term follow-up [18, 23–27]. The purpose of this study is to asses mid-term patient reported outcome measures, revision rate and radiographs of the Global Conservative Anatomic Prosthesis (C.A.P.) uncemented resurfacing shoulder prosthesis (DePuy Synthes, Warsaw, USA). This study has been performed as an extension to the ongoing follow-up study, short-term results published in 2014 [26]. The authors expect satisfactory patient reported outcome results and a revision rate lower or equal to the literature.

Patients and methods

This study was performed as an extension to the ongoing follow-up study in patients treated with uncemented Global C.A.P. resurfacing shoulder prosthesis, short-term results published in 2014 [26]. The study was approved by the Northern Dutch Review board (M1330348), and all patients had signed informed consent.

Patient population

Patients older than 18 years, with an intact and sufficient rotator cuff, adequate bone stock of the proximal humerus [>60% estimated on radiographs and magnetic resonance imaging (MRI)], with failed conservative treatment (physiotherapy, intra-articular injections with corticosteroids or arthroscopic debridement), glenoid centric type A1, A2 or B1 according of Walch classification assessed on MRI [28], and treated with a resurfacing prosthesis between January 2007 and December 2009 were included in this study. In all patients, preoperative radiographs and MRI scans were assessed. To minimize selection bias, only patients with an intact cuff and glenohumeral osteoarthritis were included.

Intervention

The senior authors performed all operations in two clinics, Alrijne Hospital (Leiderdorp, the Netherlands) and Spaarne Gasthuis (Hoofddorp, the Netherlands). All shoulders were treated with a cementless humeral resurfacing implant (Global C.A.P., DePuy Synthes, Warsaw, USA). Thirty minutes before the first incision a first-generation cephalosporin was administered intravenously. Preoperative interscalene block was used in combination with general anesthesia. Patients were placed in the beach chair position with their arm draped freely. In all shoulders, a deltopectoral approach was used. Care was taken with preservation of the tendon of the pectoralis major and the vessels of the humeral circumflex. Soft tissue releases of the tendon of the subscapularis and the anterior and posterior aspects of the capsule were performed to improve range of motion if necessary. This could also include a 360° release of the tendon of the subscapularis. The tendon of the subscapular muscle was cut close to its insertion at the minor tubercle, leaving a small part of the tendon attached. The reattachment could be done safely and strongly with multiple stitches. The construction was tested by external rotation of the arm before closure. Tenodesis or tenotomy of the long head of the biceps was only performed when tendinopathy was diagnosed intraoperatively by the senior authors. A lateral clavicle resection was performed in patients with a symptomatic AC joint diagnosed by the senior authors during physical examination prior the operation.

With respect for anatomic (retro) version and inclination the appropriate size implant was placed. Only the affected glenoid was treated with a chondropick to enhance micro fracturing of the eroded articular surface to stimulate the growth of fibrous tissue. No glenoid implants were used.

Rehabilitation

Postoperative patients used a standard sling for up to 6 weeks. Immediately, postoperative patients were stimulated to start with forward elevation and abduction and to perform front-to-back pendulum exercises. To minimize the tension in the re-attached subscapularis tendon, external rotation was allowed within the maximum degree of that obtained during surgery. Patients followed a routine rehabilitation protocol after the resurfacing shoulder arthroplasty. This protocol consisted of supervised physiotherapy for 3–6 months and self exercises.

Clinical and radiological assessment

The senior authors did the baseline assessments in all patients, including demographic details, diagnosed primary osteoarthritis, radiographs and MRI in the outpatient clinic. Two physician’s assistants (PS and MC), assessed the pain score according to the visual analog pain scale (VAS) [29, 30], the Dutch version of the Simple Shoulder Test (DSST) [31], the range of motion and strength to derive a Constant score [30, 32–37], and the patient’s activities and daily living (SF-12) [38–40]. The physician assistants did not participate in the perioperative care and did not see the postoperative X-rays.

The first day postoperative and at 3 months and annually radiographs anteroposterior and axillary were taken. Signs of loosening, such as radiolucent lines, and their evolution over time were made. Definite loosening was defined as a change in position of the implant over time. Unchanged position but progressive radiolucencies of >2 mm wide from the component were defined as probably loosening [19]. Analyses were made for luxation of the prosthesis and migration of the prosthesis outside the center of the glenoid and the length of gleno-humeral offset was assessed to measure overstuffing [41].

Statistics

For analyzing the preoperative and postoperative scores, we used Wilcoxon signed ranks test. The study data were not normally distributed, and they cannot be transformed to a normal distribution by means of a logarithmic transformation. A p value of <0.05 was considered significant. The Constant score increased and the pain (VAS) score decreased after 2 year follow-up. This can be explained by the patients with the poor scores had a revision surgery and were not included for further data analysis. To minimize selection bias, only patients with an intact cuff and glenohumeral osteoarthritis were included. Statistic software of SPSS (SPSS Inc., Chicago, Illinois, USA) version 20.0 was used.

Results

Forty-eight resurfacing humeral head surface replacement arthroplasty operations were performed in 46 patients. This cohort consists of 36 female and 12 male patients with a mean age of 72 years old (range 59–89 years). The short-term results were described in a previous publication [26].

Three patients (6%) were lost to follow-up. One patient died because of reasons not related to the prosthesis or operation. Two patients were not able to attend at the follow-up appointments due to health-related issues. The health issues were not related to the implant or operation. Eleven of 48 prosthesis (23%) had a revision operation.

Mean follow-up was 6.4 years (range 5.1–7.9). In six patients (13%), an additional lateral clavicle resection was performed. Thirty-eight patients (79%) had a biceps tenodesis and three patients (6%) had a biceps tenotomy.

The mean Constant score (corrected for gender and age [37]) improved from points 47 ± 18, preoperatively to 83 ± 22 points at follow-up (p < 0.001). The mean Dutch Simple Shoulder Test (DSST) improved from 20 ± 21 points, preoperatively to 67 ± 30 points at follow-up (p < 0.001). The pain score, according to the visual analog scale (VAS), decreased from 66 ± 19, preoperatively to 29 ± 28 points at follow-up (p < 0.001).

The SF-12, divided in a mental and a physical score, the mean SF-12 mental score improved from 49 ± 12 points preoperatively, to 51 ± 8 points at follow-up (p = 0.45). The mean SF-12 physical score improved from 35 ± 8 points preoperatively, to 39 ± 11 points at follow-up (p = 0.05). All preoperative, short-term (2 year) and mid-term follow-up data are listed in Table 1.

Table 1 Pre- and post-operative scores, n = 48
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Radiology

For 36 shoulders, radiographs were available. No loosening or dislocation were seen at mid-term follow-up. Some degree of superior migration, as an indication of rotator cuff failure or insufficiency, was noted in 15 of the 36 shoulders (42%). Six (17%) patients had severe migration and nine (25%) had mild superior migration, see Table 2. Twenty-one (58%) shoulders showed no superior migration. Moderate-to-severe glenoid erosion was present in twelve (33%) of the shoulders at a mid-term follow-up, see Table 3.

Table 2 Constant score and VAS in patients with sign of rotator cuff failure
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Table 3 Constant score and VAS in patients with glenoid erosion
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Complications

The early complications were described in the 2 year follow-up. No revision surgery was performed or necessary within the short-term follow-up [26].

Revision surgery

Eleven patients (23%), five males and six females, had a revision operation to a reverse shoulder arthroplasty or total shoulder arthroplasty, see Table 4. Mean time of revision 54 months (range 34–81 months). Mean constant score prior to revision 55 (range 28–85). Patients had a mean VAS of 59 (range 15–75) prior to revision.

Table 4 Revision surgery
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All revision surgeries were a complete revision of the resurfacing prosthesis and glenoid. All cultures taken during revision surgery were negative in the all mentioned patients, except the low grade infection. All revised patients had satisfactory results after revision surgery.

Fig. 1
figure 1

Anteroposterior X-rays of left shoulder with a Global C.A.P. resurfacing prosthesis before revision and b TSA after revision

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Discussion

The most important finding of this study of the Global C.A.P. shoulder resurfacing arthroplasty were an increase of range of motion, a reduction of pain complaints, but an increased revision rate after mid-term follow-up in contrast of 2 year follow-up [26].

Outcome assessment bias was minimized by having assessors who were not involved with the initial operation. Although we realize that TSA is the gold standard for treatment of osteoarthritis of the shoulder today [3, 42–44], we think that (short) stemmed and resurfacing hemi-shoulder prostheses are still a valid treatment option in selected patients because of the limited survival of the glenoid component in TSA after long-term follow-up. Glenoid loosening has been reported to be between 0 and 20% at medium term follow-up and 39% mid-term to long-term follow-up [6–12, 45], with more than 5% rate of revision surgery at long-term follow-up. Several factors such as rotator cuff tears, component malposition and glenoid instability can contribute to glenoid component failure [8, 45, 46].

This resurfacing prosthesis has a hydroxyapatite coating. Advantages of hydroxyapatite-coated surface replacement of the shoulder, when compared to stemmed implants, are less bone resection, primary press-fit cementless fixation with bone in-growth into a hydroxyapatite coating, easier replication of the native anatomy, reduced risk of intraoperative humeral shaft fracture and stem perforation, preservation of humeral bone stock, and easier revision surgery [19, 26, 47–49].

In line with Cofield, we think that the revision rate alone is not sensitive to a failed procedure due to the subjective assessment by the surgeon. This assessment by the surgeon should be used in combination with pain and satisfaction assessed by the patient. Especially, patients reporting pain equal or worse than their preoperative condition should also be considered as a failure [19, 50].

A resurfacing shoulder arthroplasty is less difficult to remove than a stemmed hemiarthroplasty. In contrast to Al-Hadithy and Alizadehkaiyat, our revision operations were achieved easily with the removal of the implant [24, 25]. During revision, significantly reduced bone density under the implant was observed. This observation is in line with the findings of Schmidutz et al. [5]. However, the metaphyseal bone was adequate enough to make short stem prosthesis possible. No step cut of the glenoid and bone grafting of the glenoid was necessary in all revised patients [51]. All patients had no complications and satisfactory results after revision surgery [51].

Glenoid changes after resurfacing prosthesis were assessed by measuring the joint space and determination of possible bone loss of the glenoid. This space might increase by the formation of fibrosis, because of the micro fracturing. Glenoid erosion in hemiarthroplasty is one of the major reasons for revision to total or reverse shoulder arthroplasty [52–55]. As in our study and in the literature, radiological glenoid deterioration is not correlated with pain or deterioration of clinical results [26, 41, 56, 57].

Periprosthetic fractures did not occur in our series. Possibly because of the absence of stress shielding in the midshaft with a resurfacing implant [58, 59]. A stemmed prostheses create a stress riser effect at the tip of the stem in the midshaft of the humerus [19]. Periprosthetic fractures, which have a reported prevalence of 3%, account for approximately 20% of all complications associated with total shoulder arthroplasty. This can be reduced using this prosthesis [23, 60–64].

The conclusions of this study have to be drawn in the light of some limitations. Although the patients were enrolled prospectively in a computerized database, there was no control group treated with a stemmed implant or a resurfacing prosthesis with a glenoid component as a TSP. The reported study group was small but nonetheless comparable to other published studies of shoulder resurfacing [11, 19, 22, 23]. Our revision rate (23%) was higher compared to the rate reported by Levy at al. They reported a revision rate of 14% in the resurfacing shoulder replacement after 10 years follow-up [22]. In contrast to the series reported by Streubel et al., our patients had satisfactory results after revision surgery [65].

In the literature, high rates of survival are described after mid-term and long-term follow-up. There is certainly a discrepancy in the literature with respect to revisions. Particularly recent literature from 2013 reported a significant high percentage of revisions due to glenoid erosion and pain [13, 18, 22–27, 59, 66, 67]. Relevant studies and revisions are mentioned in Table 5.

Table 5 Studies and revision rate
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Sperling et al. reported similar revision rate in a stemmed hemiarthroplasty of 22% [55]. A more recent study from Bartelt et al. showed similar results at short-term follow-up with a high rate of revision of 30% at mid-term follow-up [68].

Nevertheless, a small sample size suggests caution in interpreting the incidence of uncommon complications. Performing a “new” type of surgery on a large scale would not be considered wise because of the recent lessons we have learned from, for example, the metal-on-metal discussion in hip surgery.

Long-term and precise follow-up is essential to determine if treatment with this cementless resurfacing implant for end-stage osteoarthritis of the shoulder is viable.

Conclusion

In conclusion: we report the clinical and radiologic outcome for the uncemented Global C.A.P. resurfacing prosthesis for the treatment of primary osteoarthritis in patients with an intact rotator cuff with more than 6 years of follow-up. The mid-term of the global C.A.P. resurfacing prosthesis are in line with other studies with a concerning revision rate of 23%.