Our study showed that BIO-RSA showed improved clinical outcomes in Asian populations at mean three years follow-up as the clinical outcomes and ROM except internal rotation improved significantly. The overall rate of notching was 60.52% (23/38). However, there was no case of grade 4 glenoid notching. 100% graft incorporation and no case of glenoid loosening were observed at the last follow-up. We observed 4 intraoperative and 4 postoperative complications which are discussed further in this section.
This is the first study reporting BIO-RSA outcomes in the Asian population. Previously, few studies have reported outcomes of BIO-RSA in the Asian population. Among BIO-RSA instrumentation, large or extra-large BIO-RSA cutting guide could make thicker glenoid autograft, and these glenoid lateralization of BIO-RSA developed too much tension and difficult reduction of the prosthesis in the small sized glenoid. This was very important consideration of Asian population in BIO-RSA. We usually harvested 7 mm thickness humeral autograft and avoided 10 mm thickness autograft owing to higher tension during the proshesis reduction.
Conventional RTSA is known to produce scapular notching, less improvement in rotational movements, impingement free movements; and poor cosmesis due to medialization of the center of rotation [12]. Boileau et al [9]. originally described the method of BIO-RSA in 2011 to solve these problems. But since then, not many have adopted this technique. According to their results, the humeral autograft incorporated completely in 98% of cases (41 of 42) and partially in one. At a mean of 28 months postoperatively, no graft resorption, glenoid loosening, or postoperative instability was observed. We also had 100% graft incorporation with no glenoid loosening or instability. In their study, significantly increased active anterior elevation and external rotation at the final follow-up was noted, similar to our findings. They reported inferior scapular notching in 19% (eight of 42) and 86% (36/42) patients in their series were able to internally rotate sufficiently to reach their back over the sacrum. Although internal rotation improvement was observed in our study similar to their study with 37/38 patients being able to internally rotate to reach above the sacrum, the rate of notching was 60.5% (23/38) which is much higher than their reported rate. However, no grade 4 notching was observed and notching did not have impact on functional outcomes in our study and this rate of notching is less than the reported rates of notching with conventional RTSA (> 63%) [2, 13].
There have been few studies reporting BIO-RSA outcomes but their results reported are not similar. A comparative study between conventional and BIO- RSA was reported [14]. There was bone graft incorporation in all BIO-RSA with no evidence of graft resorption. However, the BIO-RSA technique was associated with an increase in scapular stress fracture rate when compared to the standard RSA (9.1% in the standard RSA and 16.7% in the BIO-RSA). But, this was not found to be significant (p = 0.64). We also had one case of scapular neck stress fracture which was managed conservatively. In the same study, statistically significant difference was identified when comparing the rates of scapular notching (standard RSA 68% vs BIO-RSA 33%; p = 0.028). Another study did not show any advantage of BIO-RSA over conventional RTSA including scapular notching [15]. However, their notching rate was low (5%) as compared to our study. Contradictory to this, Athwal et al.[16] reported significantly higher frequency of scapular notching (P = .022) in the RSA cohort than in the BIO-RSA cohort: 75% versus 40%, but no other outcome measures were statistically different, including range of motion, strength, and validated outcome scores in their study. All of their patients had either grade I/II notching. In our study, 87% (20/23) patients developed grade I/II notching and remaining 13%(3/23) had grade III notching with no patients showing grade IV notching. This high grade notching is much lower than reported with the conventional RTSA (> 25%).
We believe there are multiple factors to consider for notching as shown by various studies including humeral neck shaft angle, inferior overhang of the glenosphere, inferior tilting of the glenosphere, increasing glenosphere arc [4, 5]. Reason of scapular notching is usually contact between liner and bone at terminal range of motion, especially adduction and internal rotation. By using bone-graft on glenoid, there can be added advantage of relatively more impingement free motion i.e. instead of curved inferior border of glenoid, there is almost horizontal inferior border of glenoid after grafting similar to long neck scapula. This can increase impingement free range of motion to certain extent but cannot prevent liner from contacting the glenoid at terminal range of motion in adduction and internal rotation. However, further biomechanical studies are required to quantify this hypothesis. Also, higher rates of notching observed in our study as compared to other BIO-RSA studies may be because of our study population and prosthesis sizing limitation. As already quantified, the East Asian population has smaller glenoid sizes, especially females [17]. This reverse prosthesis design was not originally designed according to their morphology. All our patients received 25 mm base plate with 36 mm glenosphere which was not the case with the previous study. Athwal et al. [18] have reported 62% notching rate with 25 mm glenoid base plate (without bony increased offset) in their series which is near to our rate of notching (60.5%). Many studies have shown reduction in notching and higher impingement free adduction with larger glenosphere of diameter 42 or 44 mm rather than 36 or 38 mm diameter glenosphere which may also explain the notching rate in our study [19–23].
Boileau et al.[24] have expanded the application of BIO-RSA and reported their outcomes in glenoid deficiency using angled BIO-RSA with trapezoidal graft. However, in our study, we had three cases of severe glenoid defects, but they were managed with standard humeral head autograft (similar to trapezoidal graft) only without any complications.
As an alternative to BIO-RSA, two other lateralization options are available, metallic glenoid lateralization, and humerus lateralization. Metallic glenoid lateralization is a similar concept to the lateralized center of rotation and the results as reported by Cuff et al.[25] have been really encouraging with reduced rate (9%) for scapular notching and no glenoid loosening. However, they reported 3% asymptomatic humeral stem loosening which is a concern. Also, Harman et al.[8] reported substantially increased moment (69%) at baseplate-bone interface which may possibly lead to loosening of the baseplate and has been a particular concern with this technique of lateralization. In our study with BIO-RSA, we encountered one humeral stem loosening case. Overall rate of radiolucent lines around the humeral stem in our study was 44.74% (46.66% for cemented stems vs 25% for un-cemented stems). Though our aseptic loosening rate is similar to other studies, finding of radiolucent lines is higher than reported with conventional RTSA (15.9% for cemented stems and 9.5% for uncemented stems) [26].
The introduction of humerus lateralization has been a recent development and has shown equally good results. Franceschetti et al.[27] in their comparative study between BIO-RSA and 145° onlay curved stem showed similar clinical outcomes with equally reduced rates of scapular notching. Only improvement in the BIO-RSA group over the curved stem group significantly increased external rotation in the BIO-RSA group. However, it did not result in improved functional outcomes. The curved humeral stem provides an easier lateralization alternative technically as compared to BIO-RSA. In an analysis of 485 consecutive cases, scapular spine fractures showed increased prevalence after the humeral onlay short stem design RSA [28]. However, there are a little comparative studies and long-term comparative studies are needed to prove superiority of either method.
There were six complications in our series. The first is one case of heterotopic ossification observed on X-ray at 1.5 months postoperatively. Verhofste et al[29] et al has reported very high incidence i.e. 29.5% of heterotopic ossification following RTSA. Although this incidence is much higher than our study, the point of similarity between their study and our study is timing of the heterotopic ossification. They have reported that 81.6% of heterotopic ossification developed within first three months postoperatively, similar to our findings. Also in our study, patients with heterotopic ossification did not have an altered functional outcome as compared to other patients, similar to their finding.
The second complication was inferior screw malposition, also observed in one case. The screw was proud from the inferior aspect meaning that it was directed inferior to the inferior border of glenoid and lateral border of the scapula. However, no glenoid loosening was observed at mid-term follow-up. This was technical complication and we now prefer almost horizontal direction of the screw especially in the long neck scapula patients. The third complication was intra-operative humerus metaphyseal fracture which occurred in three patients and was treated with circumferential circlage wiring and none of the patients developed subsidence of stem. However, gradual resorption of bone noted at the medial calcar area and GT area without any sign of subsidence/ loosening on subsequent X rays.
As already mentioned previously we also noted one humeral stem loosening which developed in one of the patients with cemented stem without any sign of infection. The patient complained of occasional pain (VAS 2). On examination, there was restriction of motion (forward flexion 110, abduction 110, external rotation 20, internal rotation L4) and in radiographs, lysis around the humeral stem with rotation of the stem was noted. Infection was ruled out and patient advised revision of the stem to improve clinical outcome further. However, because of minimal complaint from the patient and advanced age (80 years), she did not want to undergo revision operation. This is similar to the aseptic loosening rate (1.18%) observed with the cemented humeral stem as reported by Gilot et al[3].
The fifth complication was one case of late infection developing 33 months after surgery. The patient was treated with PROSTALAC (antibiotic impregnated cement) insertion. And is yet to receive revision prosthesis surgery. The patient is one year postoperative after PROSTALAC insertion with healing of the wound but unable to receive the revision surgery due to aggravated comorbidities (pacemaker and age 91 years at present, the oldest patient of our study). As reported in the literature, functional outcomes of infection patients are usually poorer than primary RTSA [30], the same was the finding in our study. And the sixth complication as described previously was non-traumatic scapula fracture which developed after 27 months of primary procedure. The fracture occurred at the site medial to the tip of the glenoid screws and was minimally displaced. Kirzner et al.[14] have reported significantly higher scapula stress fracture with BIO-RSA as compared to conventional RTSA. However, our rate was much less than their series (2.6 vs 16.7%), this complication also must be considered while using BIO-RSA. The patient was managed conservatively with arm sling for six weeks. Three-month x-ray showed callus formation and there was no impact on the functional outcome.
There are few shortcomings of our study. First, we did not include a cohort to compare our data which can give more relevant analysis of a particular method with a definite conclusion. Second, we relied on X-ray to check autograft incorporation rather than performing postoperative CT scan in every patient. However, many times artefacts on postoperative CT scan also obscure perfect visualization. Third, the study design was retrospective and the number of patients (38) was small with only mid-term follow-up.