Changing societal attitudes and expectations by both surgeons and patients have resulted in earlier and more frequent surgical interventions for shoulder arthritis as patients demand more immediate pain relief after exhausting conservative measures.1 The use of traditional stemmed total shoulder arthroplasty (TSA) has substantially increased over the past decade but with loosening and revision rates on the rise,1,2 resurfacing arthroplasty, both onlay and inlay, may be an effective alternative.
Stemless onlay resurfacing arthroplasty has been available for more than 20 yr for hemiarthroplasty (HA) indications and for total shoulder resurfacing.3–6 Results with this procedure have been comparable to those of HA and TSA, with the added benefit of preservation of bone stock and simplified intraoperative geometry through the stemless design.7,8 Despite these advantages studies have reported overstuffing of the joint with onlay resurfacing arthroplasty.9,10
Inlay resurfacing is placed within the ambient joint contour, recreating the joint surface specific to its location. With its advantages of limited bone resection and ease of implantation, it is particularly indicated for patients with limited defects and otherwise healthy cartilage margins.
The purpose of the present study was to review a glenohumeral joint preservation strategy using a stemless inlay implant for the treatment of arthrosis and osteoarthritis, place these results into the context of an increasingly complex shoulder arthroplasty landscape, and report the 5-year results.
MATERIALS AND METHODS
Thirty-three consecutive patients (36 shoulders; three bilateral) with clinical and radiographic evidence of at least grade III Kellgren and Lawrence glenohumeral arthrosis that met the indications for inlay arthroplasty (IA), agreed to participate in this Western Institutional Review Board approved study. All patients provided written informed consent after the nature of the procedure was explained and were treated with HemiCAP® (Arthrosurface, Franklin, MA) IA. Two patients died of unrelated causes in the follow-up period. Three shoulders were revised (not due to implant failure), and eight patients (one bilateral) were lost before the 24-month evaluation. The remaining 22 shoulders in 20 patients constitute our study cohort. The average follow-up was 68.4 (range, 24-98) months. There were 14 men and six women with a mean age of 60.4 (range 43 to 80) years at the time of surgery.
The primary outcome was the Constant11 score at last follow-up. Secondary outcomes included radiographs; a 10-point Visual Analog Scale (VAS) (0=best) for each of the following items: stability, pain today, pain with activities, and pain at rest; the Simple Shoulder Test (SST);12 and the Short Form (SF)-36.13 Range of motion (ROM) was measured for active (AFE) and passive forward elevation (PFE) and external rotation (ER) at 90 degrees of abduction. Internal rotation (IR) was based on changes in spinal levels per Constant Score with a maximum of 10 points.
All shoulders underwent either MRI or CT preoperatively to evaluate the humeral head position, status of the glenoid, rotator cuff, and soft tissues. Standardized true anteroposterior, axillary, lateral, or scapular “Y” radiographs of the shoulder were obtained preoperatively and postoperatively. Of the original 36 shoulders, 11 were lost to follow-up and three were revised and not available for radiographic assessment. Seventeen of the remaining 22 shoulders were available for independent radiographic examination by a musculoskeletal radiologist to determine disengagement, subsidence, or tilt. Components were divided into seven radiographic zones to measure periprosthetic radiolucency according to a modified Sperling method14 (Figure 1A). An implant was determined as “at risk” if it demonstrated a 2 mm or greater periprosthetic radiolucency in three or more of the seven zones surrounding the implant.14
Of the 17, nine allowed for a comparative review of first postoperative radiograph to last follow-up. The other eight shoulders had last follow-up radiographs only. In these eight shoulders, implant subsidence or tilt was assessed using the contour of the humeral head anterior and posterior, or medial and lateral to the articular component (Figure 1B). The approach was justified as all implant sizes were partial humeral head resurfacing devices with a diameter of 30 mm (n=5), 35 mm (n=2), and 40 mm (n=1).
The preoperative and postoperative range of motion and outcome scores showed normal distribution. All data are presented as means ± standard deviations. The number and percentage of cases were used for categorical variables, and a Student t-test was used to compare mean differences between groups performed using Excel 2010 (Microsoft, Redmond, WA). P values<0.05 were considered to be statistically significant.
The HemiCAP® system consists of a two-part design that utilizes a screw fixation component and an array of articular inlay components with various diameter sizes and offsets (spherical and nonspherical) to provide a patient-specific fit. The cobalt chrome alloy articular component connects to the titanium cannulated screw-fixation post via a taper lock. Ambient shoulder anatomy, along with any unique variability, is both respected and maintained. A wide variety of pathologies, including some cases of flattening of the humeral head, are amenable to this procedure as the soft-tissue tension and intra-articular volume are less likely to be altered.
In the context of glenohumeral arthrosis, patients are good candidates for IA if the rotator cuff is intact or reparable, bone loss is minimal, and the joint is concentrically reduced in the glenoid fossa. A suggested algorithm for joint preservation in shoulder arthroplasty is presented in Figure 2.
All procedures were performed in an outpatient setting with a combination of general and regional anesthesia with patients in the beach-chair position. Prior to implantation, arthroscopic inspection evaluated and treated concurrent pathologies related to the labrum, biceps, rotator cuff, and acromioclavicular joint and staged the shoulder before proceeding to the open procedure. A detailed surgical procedure for implantation of the HemiCAP® has been described previously.15
One of the key benefits of IA is the separation of fixation and articular components. The stud screw is inserted first, allowing for subsequent assessment of the native joint morphology via intraoperative topographic measurements. Utilizing this concept maximizes the ability to precisely match the articular component volume to the implant bed volume, with minimal bone sacrifice, thereby reestablishing the geometric contour (Figure 3A and B).
A sling was utilized for 6 wk postoperatively. External rotation was limited to neutral for the first 6 wk to protect the subscapularis repair. Passive-assisted range of motion for the first 4 wk was followed by active range of motion and strengthening exercises at 6 wk. In general, unlimited active strengthening and some limited recreational pursuits were permitted at 12 wk. Patients were allowed to return to their sports activities at the 6-month mark.
For all patients, the primary indication for surgery was arthritis. Concomitant procedures included subacromial decompression in 10, distal clavicle resection in 10, repair of the rotator cuff in nine (one with an augmentation; one with plication), biceps tenotomy in 10, and tenodesis in two. Two shoulders had undergone previous surgical procedures: one repair of a superior labral tear from anterior to posterior (SLAP) and 1 combined Bankart and SLAP repair with subacromial decompression.
In eight left and 14 right shoulders, inlay implant diameters included: 2×25 mm, 9×30 mm, 7×35 mm, and 4×40 mm. All defects were completely covered by the implants inserted. No glenoid demonstrated signs of substantial bone loss or asymmetrical wear. The glenoid articular surfaces of three patients showed diffuse chondral wear patterns, ranging from grade III to IV. It was decided intraoperatively that none of the glenoids would benefit from resurfacing or reaming. The average blood loss was 50.8 cc (range 15–250 cc). One patient with a 250 cc blood loss underwent a concomitant distal clavicle resection, rotator cuff repair, and biceps tenotomy.
At last follow-up, the mean Constant score had significantly improved when compared to baseline (P<0.001). The mean SST score (P<0.001), the VAS scores for stability (P<0.001), pain today (P<0.001) and pain with activities (P<0.001) also improved significantly. The VAS score for pain at rest (P=0.4), the SF-36 physical component score (P=0.065), and the SF-36 mental component score (P=0.344) all improved but not significantly. ROM significantly improved for external rotation (P=0.04) and internal rotation (P=0.008); PFE (P=0.246) and AFE (P=0.54) improved as well, but the change was not statistically significant (Tables 1 and 2).
The mean radiographic follow-up after the index procedure in the 17 shoulders was 6.2 (range, 4-8) years. Six shoulders were treated with a 40-mm diameter implant, six with a 35-mm, and five with 30 mm. No implant at any time point met the “at risk” criteria for clinical loosening.14 At last follow-up, two shoulders showed radiolucency of 2 mm or greater in two of seven evaluated zones on anteroposterior views; corresponding axillary views showed no radiolucency in all of the seven evaluated zones and therefore did not meet the “at risk” definition. All other devices had no radiographic radiolucency of 2 mm or greater in any zone on any view.
None of the cases at any time point demonstrated visible (n=8) or progressive (n=9) subsidence or tilt. None of the devices showed a disengagement of the fixation component from the articular component (Table 3). Subset comparison of preoperative to postoperative radiographs showed no sign of radiographic progression of osteoarthritis.
Three of original 36 shoulders were revised in the study. One patient developed stage IV metastatic cancer to the humerus subsequent to the index surgery and had revision to a stemmed implant. Another patient had a motor vehicle accident 3 mo after surgery that resulted in nerve and vascular injury to her ipsilateral arm. She was treated surgically for the neurovascular injuries and subsequently developed a series of complications that included tearing of the subscapularis and thrombosis in the affected arm. This patient was eventually treated with a reverse TSA. Another patient reported ongoing and progressive pain and required conversion to a traditional TSA. None of the revisions were attributed to a failure of the HemiCAP® implant. No further evaluations were performed after their revision procedures.
Our study showed few revisions in our small cohort of patients treated with IA. These patients achieved significant clinical improvement at an average follow-up of 5 yr using stemless IA. Although range of motion was not significantly better for AFE or PFE, all patients did show improvement with significantly better internal and external rotation. No implant was found to be “at risk,” and no progression of degeneration was seen.
Stemless IA was first introduced in 2004 as a small-diameter implant intended to treat focal chondral lesions of the proximal humerus. The system has evolved over time with a complete range of diameters from small to full head resurfacing. In the procedures described in this study, only partial IA components in sizes ranging from 25 to 40 mm diameter were used because those were the sizes available at the time.
Apart from the technical advantages of IA, the ability to completely cover the defect remains the primary determinant in selecting patients for the procedure. By resurfacing the humeral defect, the coefficient of friction against the glenoid is lowered and may aid in pain relief. Secondary pain generators such as synovium, loose bodies, rotator cuff, biceps, glenoid, labrum, acromioclavicular joint, and the subacromial space must undergo careful preoperative and intraoperative assessment and treatment to maximize patient benefit and surgical success. Consideration of implant longevity, especially for younger patients, plays a critical role when making primary arthroplasty decisions.
Hammond et al.,16 compared IA to stemmed HA in a biomechanical study.16 IA more closely restored the geometric center of the humeral head, with less eccentric loading of the glenoid. They concluded that IA may limit eccentric glenoid wear and permit better functionality because the glenohumeral joint biomechanics and the moment arms of the rotator cuff and the deltoid muscle are restored more closely to those of the intact condition.
The clinical results of our 5-year study reconfirm earlier reports with longer follow-up. Scalise et al.17 reported favorable short-term clinical outcomes for their 62 patients who had a mean age similar to our series of 60 yr. They found no evidence of osteolysis, radiolucency, or loss of fixation at 8 mo after surgery, and 95% of their patients reported good-to-excellent results using the same implant. In another study, Uribe and Bemden18 reported 11 patients (12 shoulders) with a mean age of 56 yr, treated with inlay resurfacing arthroplasty for advanced osteonecrosis of the humeral head. At an average follow-up of 30 mo, the authors reported significant pain relief and functional improvement (P<0.001). In a retrospective case series of 20 shoulders with an average follow-up of 33 mo, Sweet et al.19 also reported significant pain relief, functional improvement, and patient satisfaction using HemiCAP® IA. The authors concluded that the procedure is a promising new direction in primary shoulder arthroplasty.
Our mid-term study is in direct contrast to Delaney et al.20 who hypothesized that partial humeral head resurfacing does not offer a reasonable alternative to complete humeral head resurfacing or TSA. In this level IV series of inlay glenohumeral arthroplasty for focal chondral defects in a young cohort of patients (average age 45.6 yr; range 27–76 yr) followed for a mean of 51.3 mo, they reported a 64% success rate in 39 shoulders, 35 of which had multiple pathologies that did not include osteoarthritis. It is our impression that a two-thirds success rate in treating complex pathologies in young shoulder patients and avoiding stemmed arthroplasty may be an impetus to further define resurfacing indications but not an indictment of the efficacy of the resurfacing procedure itself.
When compared with all other arthroplasty categories, the 2015 Australian Shoulder Arthroplasty Registry showed the lowest revision rate (RR) per 100 observed implant years (RR, 0.57) for partial humeral head resurfacing (HemiCAP®).21 The registry report also showed a considerable trend toward an increased RR in younger patients treated with stemmed arthroplasty (>75 yr RR of 1.52; <65 yr RR 2.29, 51% increase;< 55 yr RR 2.6, 74% increase) or onlay hemiarthroplasty (>75 yr RR 1.42; <65 yr RR 3.22, 126% increase <55 yr RR 2.49, 75% increase). Other arthroplasty classes showed similar trends (Figure 4).
There is a need for less invasive alternatives to TSA when considering the long-term radiographic results of stemmed procedures. Raiss et al.22 reviewed radiographic outcomes of 329 shoulders treated with TSA at a mean follow-up of 8.2 yr and found evidence of subsidence in 38% (125 shoulders). They also reported that 66.9% had evidence of radiolucent lines (mean, 2 points; range, 0–6 points) on immediate postoperative radiographs. Osteolysis of the greater tuberosity, calcar, or a combination of both occurred in 94.5% of the shoulders with loose glenoids. Our long-term independent radiographic data demonstrated excellent fixation at a post-implantation follow-up ranging from 4 to 8 yr with no subsidence, tilt, disengagement, progression of osteoarthritis, or any significant periprosthetic radiolucency. Several reports have indicated that both onlay hemiarthroplasty and TSA may lead to overstuffing of the joint. Inadvertent varus alignment of the prosthesis in order to avoid interference with the rotator cuff insertion has been proposed as a factor.9,10 In addition, spherical prosthetic heads cannot accurately replicate the native nonspherical humeral head morphology.23 The use of the larger superoinferior humeral head diameter for implant sizing to effectively cover the humeral head is adding nonphysiological surface volume to the smaller anteroposterior dimension when spherical prosthetics are implanted. Reconstructing “normal” shoulder morphology may lead to a nonphysiological increase in intraarticular volume. As a result, elevated tissue tension may lead to pain and dysfunction from overstuffing. IA may avoid the risk of overstuffing with congruent restoration of the native joint surface.
There were limitations to this study. The lack of a control group and a small sample size may detract from the generalizability of the results. The heterogeneity of the case series limited our ability to determine if the improvements seen were from the arthroplasty procedure or the concomitant treatments. However, significant improvements were seen in all patients, even those without concomitant procedures. The radiographic follow-up was incomplete; however, we thought it was noteworthy to report the 17 of 22 radiographs that were available.
Stemless IA is a safe and effective primary procedure for symptomatic glenohumeral degeneration that shows significant pain reduction and functional improvements at a mean of 5 yr follow-up. Although the evidence continues to grow, larger cohorts with indication-specific analyses are required to further establish this technique as a primary glenohumeral arthroplasty in patients who would benefit from the advantages of joint preservation.
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Keywords:Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved
stemless inlay arthroplasty; cartilage defect; shoulder arthroplasty; HemiCAP