Effect of glenoid perforation during total shoulder arthroplasty on glenoid component cement fixation and suprascapular nerve

Abstract

Background

Arthritic glenoids are susceptible to vault perforation during total shoulder arthroplasty. We investigated the effects of glenoid perforation and subsequent cement extrusion on the suprascapular nerve and on the glenoid cement infiltration.

Methods

Total shoulder arthroplasty using three-pegged glenoid components were performed on 10 cadaveric shoulders assigned to two groups (perforation vs. control). In perforation group, the glenoids were reamed eccentrically and intentionally perforated medially through the central peg hole, whereas control group received perpendicular reaming with no perforation. Bone cement was applied to each peg. Spatial relationship between the extruded cement and the suprascapular nerve, and the amount of cement infiltration into the cancellous bone were evaluated.

Results

In perforation group, five specimens were perforated anteriorly, and two posteriorly. In the two posteriorly perforated specimens, the suprascapular nerve was in direct contact with extruded cement at the spinoglenoid notch. Perforation group showed significantly less cement infiltration into the cancellous bone than control group (p = 0.008).

Conclusions

Glenoid perforation decreases the volume of cement infiltration into the cancellous bone potentially compromising glenoid component fixation. Glenoid perforation tends to occur anteriorly rather than posteriorly in arthritic glenoids; however, if perforation occurs posteriorly, the suprascapular nerve is at immediate risk from the extruded cement.

Level of evidence: Basic science study.

Introduction

Glenoid component loosening is the most common complication associated with total shoulder arthroplasty (TSA), comprising 32% of all complications and 7% of all indications for revision surgery. ¹ While glenoid component failure is dependent on many factors, improved cementing technique in particular has been shown to improve glenoid fixation and reduce the rate and extent of glenoid radiolucency associated with aseptic loosening.^2–5 Interposition of fluid or clot between the cement and the glenoid bone compromises the quality of fixation of the glenoid component, as does failure of cement to infiltrate into the cancellous bone. ⁶ Many patients undergoing TSA have severe glenoid erosion and are susceptible to glenoid vault perforation medially during drilling of glenoid-peg receiving holes. ⁷ Studies show that extrusion of bone cement from peg-receiving holes through a perforated medial cortex during insertion of a glenoid component is not an uncommon finding.^7,8 However, little is known about the effect of glenoid perforation on the cement fixation of a glenoid component. Furthermore, in cases of glenoid perforation, the spatial relationship of extruded cement with the surrounding anatomical structures, especially the suprascapular nerve, which is in close proximity to the glenoid vault, has not yet been investigated. There are no previous reports in the literature that have described a suprascapular nerve injury caused by extruded cement following TSA; however, we have experienced a clinical case where a patient whose TSA had been complicated by intraoperative glenoid perforation and cement extrusion later developed a postoperative suprascapular nerve palsy resulting in rotator cuff dysfunction (Figure 1). The patient had 26° retroversion as well as substantial medialization of the glenoid preoperatively. At six weeks following TSA, the patient started showing clinical evidence of infraspinatus muscle atrophy and was unable to actively elevate the arm more than 45°. This patient subsequently underwent revision to reverse TSA and ultimately achieved satisfactory results.

Figure 1.

Radiograph (left) and CT scan (right) images of a patient whose glenoid were perforated intraoperatively leading to subsequent cement extrusion to the spinoglenoid notch. The patient developed suprascapular nerve palsy and rotator cuff dysfunction postoperatively.

The purpose of this study was to investigate the effects of glenoid perforation and subsequent cement leakage on the initial fixation quality of pegged glenoid components by quantitatively analyzing the cement infiltration into the cancellous bone within the glenoid vault, and to investigate the spatial relationship of extruded cement to the suprascapular nerve in cadaveric shoulder specimens. We hypothesized that glenoid perforation would result in decreased cement infiltration on micro-computed tomography (micro-CT) imaging, and that extruded cement would be in close proximity to the suprascapular nerve if the glenoid vault is perforated through the posterior cortex.

Methods

Cadaveric specimen preparation

TSAs were performed in two groups of unpaired fresh frozen cadaveric shoulder specimens (total n = 10, average age of donors = 62 years) with no arthritic changes or deformities. The specimens were completely thawed at room temperature for at least 24 h to ensure that the specimens reached room temperature (23℃) prior to the experiment. Specimens were randomly assigned to two groups; the control group (n = 3) was comprised of specimens with no perforation of the glenoid, while the perforation group (n = 7) was comprised of specimens with glenoid perforation. In the perforation group, we simulated an arthritic glenoid by eccentrically reaming the posterior glenoid more than the anterior glenoid to create approximately 15° of retroversion as described previously by Kim et al. ⁹ In both groups, each specimen was prepared for routine TSA by the attending surgeon according to the standard surgical technique utilizing a deltopectoral approach. The humeral head was resected at the level of the anatomic neck, but no humeral component was implanted. After removal of the biceps tendon and labrum from the glenoid, a glenoid drill guide for three-pegged glenoid components (Biglani/Flatow, Zimmer, Warsaw, IN) was positioned on the geometric center of the glenoid. A 6-mm glenoid drill was then placed on the glenoid face to make a unicortical hole at the center of the glenoid for the central peg of the glenoid component. The glenoid face was reamed with a 46-mm glenoid reamer to obtain a conforming glenoid surface to the back surface of a 46 × 46 mm glenoid component (i.e., 46-mm outer diameter and 46-mm diameter of curvature). In the control group, the glenoid reaming was performed perpendicular to the glenoid face. On the other hand, in the perforation group, the reaming was performed in a 15° retroversion using a custom-made angle guide and was continued until the newly reamed surface covered the entire glenoid face. Two additional peg holes were made superior and inferior to the central peg hole, respectively. The central peg was 1.5 cm long, and the superior and inferior pegs were 1 cm long. In the control group, an intact glenoid cavity was confirmed prior to glenoid component implantation by probing the drill holes with a pair of forceps and ensuring an intact medial wall. In the perforation group, the central peg hole was drilled further medially to breach the medial wall while the superior and inferior holes were kept intact.

Suprascapular nerve dissection in perforation group

Following glenoid drilling, the scapular neck area of each specimen was carefully dissected to identify the suprascapular nerve at the suprascapular and spinoglenoid notches in the perforation group. A 1.6-mm Kirschner wire was inserted through the perforated central peg hole to mark the location of the perforation of the glenoid vault, and the location of the suprascapular nerve was inspected in relation to the location of the perforation. The local anatomical structures including the overlying supraspinatus and infraspinatus muscles were kept intact as much as possible.

Cementing technique

Palacos® R 1 × 40 bone cement (Zimmer Biomet, Warsaw, IN) was prepared in a mixing bowl according to the manufacturer’s directions and then applied with a 50-ml syringe to the glenoid peg holes in each specimen. The cement was pushed into the holes by manually pressing the plunger of the syringe. The same volume of cement was used for each specimen. For cement pressurization, the cement was pressed into the hole with a straight Adson clamp with an edge of a gauze sponge in the jaws of the clamp as described in a previous study. ⁶ These steps were repeated for a second time. Cement was then applied for a third time with the same syringe and pressurization with the plunger, and the glenoid component was pressed into place with the surgeon’s finger until the cement hardened. In the perforation group, cement was applied to the perforated central holes using only one-time manual plunger pressurization in order to reflect a real clinical setting where the operating surgeon would try to avoid overzealous cement pressurization into the holes that are found to be perforated. All cement application was done by the attending surgeon with a similar manual pressure as would be done normally in a real surgical setting.

Measurement of the quantity, location, and temperature of extruded cement in perforation group

A fine thermal probe (Needle Thermocouples SE319, TECPEL Co., Taiwan) was inserted through overlying supraspinatus muscle to the surface of the extruded cement medial to the scapular neck to measure the temperature of the cement in real time every 30 s as it cured while the deeper structures were kept intact. After complete cement curing, the spatial relationship between the extruded cement and the suprascapular nerve was evaluated by inspecting the direct distance between them and the pattern of cement position relative to the nerve. Lastly, the extruded cement was removed right at the perforation site and the specimens were subjected to subsequent micro-CT measurement.

Micro-CT measurement

After the cement was fully cured, the implanted glenoid vault was separated from the body of the scapula using a sagittal saw to fit into an 80-mm micro-CT bore. Micro-CT was performed using a SCANCO vivaCT 40 (Scanco Medical AG, Brüttisellen, Switzerland) with a field-of-view of 40 mm in diameter, and slice thickness and voxel resolution of 19 µm. We then measured the following variables in the cement adjacent to the central peg hole using three-dimensional reconstruction software (Mimics, Materialise) based on the approach described by Flint et al.: ⁶ cement volume distributed around the central peg to the medial end of the peg, cement volume distributed around the central peg to the medial end of the glenoid specimen, mean radius and maximum radius of the cement mantles surrounding the glenoid pegs, and the volume of cement extruded out of the glenoid.

Statistical analysis

The sample size of the proposed study was based on a previous study ⁶ where statistical significance was found when similar micro-CT variables were compared between three different cementing technique groups. There were five specimens in each group (n = 15) in the study. We compared the two groups in regards to the surface area, volume, depth of infiltration, cortical contact, mean radius, and maximum radius of each of the cement mantles in each of the superior and central peg holes using Mann–Whitney U test. In regards to the spatial relationship between the cement and suprascapular nerve, and the temperature changes at the surface of the extruded cement, only descriptive statistics were obtained. Statistical significance was set at p < 0.05.

Results

During the removal of the glenoid for preparation for micro-CT, one of the perforation group glenoids was accidentally broken lateral to the medial extent of the central peg of the glenoid component and was unable to be used for micro-CT analysis. This specimen was excluded from the cement infiltration data analysis.

Dissection of the seven Perforation group specimens after cement pressurization revealed that the direction of cement extrusion in the Perforation group was anterior to the scapular neck in five shoulders and posterior in two shoulders. In the two shoulders with posterior cement extrusion, the suprascapular nerve was found to be in direct contact with the extruded cement just inferior to the spinoglenoid notch (Figure 2). The suprascapular nerve was found almost completely surrounded by the extruded cement in one of those two specimens (Figure 3). In the five specimens with anterior cement extrusion, the extruded cement was found to be located deep to the subscapularis muscle and inferior to the suprascapular notch by a distance of 14 mm or less. The upper and lower subscapular nerves were superficial to the subscapularis muscle and were therefore protected from the extruded cement by the interposing subscapularis muscle.

Figure 2.

In this specimen with glenoid perforation, the extruded cement (*) is in direct contact with the suprascapular nerve (blue arrow) immediately inferior to the spinoglenoid notch.

Figure 3.

In this specimen with glenoid perforation, the suprascapular nerve (blue arrow) is completely encased by the extruded cement (*).

The average volume of the extruded cement out of the glenoid was 2.9 ± 4.6 cm³, and there was no significant difference of the volume between the specimens with anterior extrusion and the ones with posterior extrusion (p > 0.05). The maximum curing temperature of cement was 95.9℃ when measured in a cement mass, while the mean temperature measured on the surface of the extruded cement was 39.6℃. In comparison of the amount of cement infiltrated into the trabecular bone surrounding the central peg within the glenoid vault, there was a significantly lower volume of cement infiltration in the perforation group (268.6 ± 151.4 mm³) than in the control group (632.4 ± 100.8 mm³) measured along the entire length of the central peg (p = 0.008; Figure 4 and Table 1). Similarly, when measured to the medial end of the glenoid vault, the volume of cement infiltration was significantly lower in the perforation group (288.1 ± 165.3 mm³) than in the control group (859.1 ± 350.1 mm³; p = 0.01). There was no significant difference in glenoid bone density between the two groups (p = 0.88).

Figure 4.

Micro-CT images of cemented glenoids at the mid-level of the central peg demonstrating infiltration of the cement into the trabecular bone of the glenoid vault in a perforated (a) and non-perforated glenoid (b).

Table 1.

Micro-CT measurement data.

	Perforation group (n = 6)	Control group (n = 3)
Volume of cement infiltrated into adjacent cancellous bone (measured to the end of central peg)	268.6 ± 151.4 mm3	632.4 ± 100.8 mm3	p = 0.008
Volume of cement infiltrated into adjacent cancellous bone (measured to the medial end of glenoid)	288.1 ± 165.3 mm3	859.1 ± 350.1 mm3	p = 0.01
Volume of cement extruded out of glenoid	2.9 ± 4.6 cm3	Not applicable
Mean radius of cement mantle surrounding the glenoid pegs	8.0 ± 1.5 mm	11.2 ± 0.9 mm	p = 0.01
Bone density (bone volume/total volume)	0.3 ± 0.1	0.3 ± 0.1	p = 0.88

Discussion

The true incidence of glenoid vault perforation during anatomic TSA is unknown. Glenoid perforation may be underreported as surgeons cannot always feel a breach of the medial cortex while drilling the glenoid intraoperatively. Glenoid perforation seems to be sometimes inevitable in patients with small native glenoids, and these glenoids are further compromised by excessive glenoid retroversion or medialization.^7,8 There is not enough bone stock to prevent perforation during glenoid preparation in these patients. Furthermore, asymmetric reaming to restore neutral version of the glenoid may decrease available bone stock. With the advances in materials and technologies, pegged-glenoid components that do not require cementing for the central peg have been introduced. These components may reduce the concerns from cement extrusion through central peg perforation, but cement extrusion through peripheral peg hole perforation still remains an issue. While several studies^2–5,10 have evaluated cement infiltration in the glenoid vault and associated factors such as cementing technique and pressurization that affect the quality of component fixation, to our knowledge, no studies have investigated the effect of glenoid perforation on cement infiltration into the cancellous bone of the glenoid vault. While we hypothesized that glenoid perforation would affect cement fixation of the glenoid component, we also hypothesized that cement extruded through the posterior cortex of the glenoid vault would pose a substantial injury risk to the suprascapular nerve, which lies directly on the bone between the suprascapular and spinoglenoid notches. The temperature during the exothermic polymerization process of cement curing can reach 82–86℃, which well exceeds the threshold for a thermal nerve injury.^11–13

The results of our study suggest that perforation of the medial cortex of the glenoid vault results in a significantly decreased volume of cement infiltrated into the cancellous bone adjacent to the component pegs. Even with no attempt to pressurize cement into the perforated hole, the simple act of putting cement in the hole caused a substantial volume of cement to be extruded medially. For optimal cement pressurization, it is critical that cement is pressurized into a closed space (i.e., a contained peg hole). If a hole is open medially due to glenoid perforation, no effective pressurization can be achieved. If one tries to pressurize cement into a perforated hole, a significant amount of cement will be extruded medially. Cement that is extruded into the posterior aspect of the scapular neck comes in close proximity to the adjacent suprascapular nerve in the area adjacent to the spinoglenoid notch, and has the potential to result in a thermal injury to the nerve. An anatomic study by Bigliani et al. ¹⁴ showed that the distance from the supraglenoid tubercle to the suprascapular nerve is on average within 3 cm at the suprascapular notch and 2.5 cm at the base of the scapular spine. Among the seven specimens with simulated posterior eccentric glenoid wear and retroversion included in our study, only two specimens had a posterior perforation resulting in posterior cement extrusion, while all other specimens had anterior cement extrusion into the subscapular fossa. Anteriorly extruded cement was located deep to the subscapularis muscle, and the muscle acted as a protective barrier that separated the subscapular nerves from the extruded cement. It can be extrapolated that anterior cement extrusion may occur more often than posterior extrusion during TSAs in osteoarthritic glenoids; however, it should be noted that, in both specimens with posterior extrusion, the suprascapular nerve was found to be in direct contact with or completely encased by the extruded cement, dramatically increasing the risk of injuring the nerve.

There are only a few published studies in the literature that have investigated the clinical effects of glenoid perforation during TSA. Hsu et al. ⁷ reported a retrospective case–control study where the clinical and radiographic outcomes were compared between 25 patients with glenoid perforation and 25 patients with no such perforation. At an average follow-up of more than five years, glenoid component loosening did not occur in any cases in which the central or peripheral pegs of a pegged glenoid component violated the medial cortex. They found that shoulder function was significantly lower in patients with perforation, although pain relief and satisfaction were similar between the two groups. The authors speculated that patients with glenoid perforation had more severe arthritic changes (e.g., more severe retroversion, medialization, and soft tissue imbalance) potentially leading to the inferior level of shoulder function. It should be noted though that the glenoid components used in their study (Anchor Peg Glenoid; DePuy Synthes, Warsaw, IN) employed a press-fit central peg that does not require cementing and three cemented peripheral pegs. Therefore, there was no cement extrusion through the central peg. The study did not report if there was any cement extrusion through any of the peripheral pegs. In their retrospective case–control study, Press et al. ⁸ reported the clinical outcomes of 18 TSA patients with glenoid perforation. All patients in this study received cemented four-pegged glenoid components. Perforations occurred through a single peg-receiving hole in 11 patients, through two holes in 6 patients, and through three holes in 1 patient. The most commonly perforated hole was the superior hole (13 patients), and three perforations took place through the central hole. The study reported satisfactory short-term outcomes at an average follow-up of 28.1 months that were comparable to a control group with no such perforation, and there were no neurologic complications from extruded cement.

Our study has several important limitations. First, our study was a time-zero cadaveric experiment mainly evaluating the quantity of cement infiltration into the cancellous bone. It was not designed to evaluate the biomechanical strength of glenoid fixation or the long-term clinical effects of glenoid perforation. Although the study by Press et al. ⁸ reported satisfactory short-term clinical and radiographic results of 18 TSA patients who had intraoperative glenoid perforation with an average of 28-months of follow-up, the long-term clinical consequences of glenoid perforation still remain unknown. Second, our study simulated only one central peg hole perforation, which can be different than the real clinical setting where glenoid perforation can occur through more than one peg hole, as the studies of Press et al. ⁸ and Hsu et al. ⁷ have described. The consequences of perforation in peripheral peg holes and subsequent cement extrusion might have been different from the central peg hole perforation, but this was not investigated in our study. It should be noted that some pegged-glenoid components available in the market do not require cementing for the central peg and may reduce the concerns about cement extrusion through central peg perforation. But, cement extrusion through peripheral peg hole perforation can still pose an issue. Glenoid component designs with peripheral pegs that are anterior and posterior commonly get peg perforations in these locations, particularly in the posterior peripheral peg of a retroverted glenoid. These more peripheral posterior perforations would cause posterior cement extrusion, but likely in a different location relative to the suprascapular nerve than a more central posterior perforation. Third, our temperature measurement method might not have reflected the true curing temperature of extruded cement. The overlying anatomical structures such as the muscles and connective tissue had to be exposed and reflected in order to place a temperature probe on the surface of extruded cement, which might have underestimated the curing temperature that would have occurred within a completely contained space in a real clinical setting. Fourth, in vitro cementation in cadaveric specimens may differ from cementation in a living patient as the glenoid of a living patient may have a greater bone density and intraosseous pressure that may limit cement infiltration. ⁶ Fifth, the actual glenoid version of the specimens was not measured in the present study. It was simply assumed that the control group had neutral version, and the perforation group had 15° retroversion. Lastly, this study had a small sample size with an uneven number of specimens included in two groups. It would have been ideal if paired specimens had been used and divided equally between the groups. Additionally, we attempted to investigate two factors (i.e., the perforation pattern in retroverted glenoids and the amount of cement infiltration within the glenoid) simultaneously with a limited number of specimens, and this made it difficult to separate the isolated effect of perforation on cement infiltration. The sample size was based on a previous study that conducted a similar analysis and showed statistically significant differences. We acknowledge that the small sample size can raise a concern for a possible β error, but this sample size did allow us to detect statistically significant differences in the cement infiltration volume between the two groups obviating the concern.

In summary, this study found that glenoid vault perforation during TSA decreases the ability to pressurize cement into the surrounding cancellous bone, potentially decreasing the fixation strength. Perforations in retroverted arthritic glenoids are more likely to occur through the anterior cortex of the glenoid vault than through the posterior cortex. However, if a perforation does occur through the posterior cortex, the extruded cement can place the suprascapular nerve at immediate risk of thermal and mechanical injury.

ORCID iDs

Connor L Zale https://orcid.org/0000-0001-7610-5528

H Mike Kim https://orcid.org/0000-0002-5286-5335