Heinz R. Hoenecke

Accuracy of CT-based measurements of glenoid version for total shoulder arthroplasty

BACKGROUND/HYPOTHESIS The arthritic glenoid is typically in retroversion and restoration to neutral version is recommended. While a method for measurement of glenoid version using axial computed tomography (CT) has been reported and has been widely accepted, its accuracy and reproducibility has not been established. METHODS In 33 patients scheduled for shoulder arthroplasty, glenoid version and maximum wear of the glenoid articular surface were measured with respect to the scapular body axis on 2-dimensional- (2D) CT slices as well as on 3-dimensional- (3D) reconstructed models of the same CT slices. RESULTS Clinical CT scans were axially aligned with the patients torso but were almost never perpendicular to the scapular body. The average absolute error in version measured on the 2D-CT slice passing through the tip of the coracoid was 5.1 degrees (range, 0 - 16 degrees , P < .001). On high-resolution 3D-CT reconstructions, the location of maximum wear was most commonly posterior and was missed on the clinical 2D-CT slices in 52% of cases. CONCLUSION Error in measuring version and depth of maximum wear can substantially affect the determination of the degree of correction necessary in arthritic glenoids. Accurately measuring glenoid version and locating the direction of maximum wear requires a full 3D-CT reconstruction and analysis.

Optimizing glenoid component position using three-dimensional computed tomography reconstruction

Glenoid implant design and alignment are critical to the success of shoulder arthroplasty. Computer-aided design models of 3 glenoid implant designs (keel, standard pegs, and modified pegs) were virtually implanted into 3-dimensional computed tomography-reconstructed models of 40 normal scapulae. The incidence of perforation on 3-dimensional computed tomography preoperative templating varied from 8% to 18% for the 3 models. Malalignment of the implants in retroversion was better tolerated than anteversion and varied with implant design. Tolerance for medialization of the implant to correct for glenoid wear was limited (range, 0 degrees-18 degrees ) and varied with implant design. The modified peg design had the lowest incidence of perforation, the greatest tolerance for malalignment, and the ability to correct for glenoid wear effects. These results emphasize the need for accurate preoperative templating and for developing alignment guides or surgical navigation tools for shoulder arthroplasty and may be used to improve implant fixation designs.

In vivo changes after mechanical injury.

Chondrocytes undergo apoptosis in response to mechanical injury in vitro. The current clinical study correlates arthroscopic and magnetic resonance imaging results with biopsy specimens of cartilage from patients with knee injury. Twenty patients were evaluated at a mean 2.7 months after acute knee injury. The mean age of the patients was 32 years and the mean weight was 83 kg. Cartilage lesions were graded separately on magnetic resonance images and arthroscopy in a blinded manner. During arthroscopy, a 1.8 mm diameter biopsy specimen was obtained from the edge of cartilage lesion. The biopsy specimen underwent histologic examination by safranin O staining and detection of chondrocyte apoptosis by the presence of deoxyribonucleic acid fragmentation. There was a positive correlation in 50% (10 of 20) when the presence or absence of cartilage lesions by magnetic resonance imaging was correlated with arthroscopy. All cases of partial thickness or full-thickness cartilage loss that were seen by arthroscopy also were detected by magnetic resonance images. Apoptotic cells were significantly more numerous in biopsy specimens from lesions compared with control biopsy specimens. The findings of reduced cell viability attributable to apoptosis may have profound implications for cartilage repair. This opens potential therapeutic avenues for the treatment of posttraumatic cartilage lesions through apoptosis prevention.

Glenoid morphology rather than version predicts humeral subluxation: a different perspective on the glenoid in total shoulder arthroplasty

BACKGROUND Glenoid retroversion is thought be important in shoulder stability before and after shoulder arthroplasty; thus, many authors recommend glenoid reaming to correct retroversion and improve stability. Genetic analysis has revealed that glenoid vault and scapular development are controlled by different genes and environmental factors, resulting in diverse glenoid morphologies. We therefore analyzed the relative contribution of glenoid morphology and version to humeral head position. MATERIALS AND METHODS We obtained 121 shoulder computed tomography scans preoperatively for shoulder arthroplasty. Humeral subluxation and glenoid version were measured on the axial image at the middle of each glenoid. Glenoid morphology was characterized as biconcave, worn, displaced, dysplastic, angled, or neutral. The strength of the correlation between humeral subluxation, glenoid version, and glenoid morphology was analyzed. RESULTS Glenoid version did not correlate with humeral subluxation. The highest frequency of posterior subluxation was noted in biconcave glenoids. Shoulders with other glenoid morphologies were more likely to have anterior or central positioning of the humerus. The mean subluxation ratio for biconcave glenoids was 0.56 and was significantly different from all other morphologies (P < .02). DISCUSSION/CONCLUSION Even in the arthritic shoulder, glenoid orientation does not appear to explain the complex biomechanics of shoulder stability. The causes of humeral head subluxation before and after total shoulder arthroplasty are likely multifactorial and may include static and dynamic soft-tissue forces. The biconcave glenoid deserves more attention at surgery because of the high association with posterior subluxation.

Effect of Osteochondral Graft Insertion Forces on Chondrocyte Viability

Background Because chondrocytes are responsible for articular cartilage matrix synthesis and maintenance, reduced chondrocyte viability could compromise graft survival, healing, and clinical outcome. Hypothesis Typical forces used in osteochondral grafting reduce the viability of the chondrocytes in the graft. Study Design: Controlled laboratory study. Methods Osteochondral grafting was performed in 4 fresh-frozen cadaver knees (n = 16 per knee). Impact force was measured during extrusion of the donor graft from the harvester into the recipient site, seating the graft flush with the articular surface of the surrounding cartilage using a tamp, and recessing the graft surface below the recipient articular surface. The magnitudes of forces measured during cadaver surgery (200,400, and 800 N) were reproduced using a drop-tower apparatus on 80 fresh osteochondral grafts harvested from knee blocks provided by tissue banks. Cell viability and glycosaminoglycan release in media were measured at 48 hours after injury. Results Forces were relatively low (range, 124-356 N) during graft extrusion from the harvester into the recipient defect or during flush seating (range, 191-418 N) of the graft. Attempts to recess the graft generated significantly greater force (range, 147-685- P < .01). When the donor graft length was 2 mm longer than the depth of the recipient hole, the mean impact force generated was even higher (range, 240-1114 N) than the force seen in a donor graft of equal length. No reduction in viability was seen at 200-N and 400-N impacts. However, a significant decrease in chondrocyte viability was seen in the group impacted with 800 N (only 50% of cells were viable, compared with 91 % in the sham group; P < .01). Glycosaminoglycan levels in culture media did not correlate significantly with insertion force. Conclusion Typical graft insertion forces did not significantly reduce chondrocyte viability. However, increased graft length relative to the depth of the recipient hole and attempts to recess the graft generated higher forces, which reduced chondrocyte viability. Clinical Relevance Any theoretical benefits of cancellous bone compaction that may occur in grafts that are recessed or are longer than the recipient holes must be balanced against the potential reduction in chondrocyte viability.

The efficacy of continuous bupivacaine infiltration following arthroscopic rotator cuff repair.

PURPOSE This prospective, randomized, double-blind study with a placebo group and 2 experimental groups evaluated the efficacy of continuous low-dose bupivacaine infiltration by infusion pump after arthroscopic rotator cuff repair. METHODS Sixty patients undergoing arthroscopic rotator cuff repair received a bolus injection in the subacromial space of 35 mL of 0.25% bupivacaine with 1:200,000 epinephrine at surgical closure and were randomized to 1 of 3 groups: 0.25% bupivacaine at 2 mL/hr (n = 20), 0.25% bupivacaine at 5 mL/hr (n = 20), or saline at 5 mL/hr (n = 20) via infusion pump into the subacromial space. Pain was evaluated using the visual analog scale (VAS) and narcotic consumption was measured until 48 hours after surgery and converted to dose equivalents (DE). RESULTS Sixty patients used the infusion pump for a mean of 43.9 hours (range, 15.50 to 50.75 hrs). Mean total narcotic consumption, expressed in DEs, was 2.24 for the 2-mL group, 3.52 for the 5-mL group, and 2.32 for the placebo group. Mean pain score was 2.9 for the 2-mL group, 3.6 for the 5-mL group, and 3.3 for the placebo group. There were no differences in operating room time or infusion pump use time among groups. The 2-mL group had a nonsignificant trend toward less pain and lower narcotic consumption. The 5-mL group evidenced a nonsignificant trend toward more pain and higher narcotic consumption. CONCLUSIONS This study neither supports nor refutes the use of infusion pumps. We hypothesized that the placebo group would experience greater pain than the 5-mL group; however, a nonsignificant trend toward the contrary occurred. A trend toward less pain in the 2-mL group was not significant. LEVEL OF EVIDENCE Level II, randomized controlled trial of therapeutic treatment that lacks statistical significance and narrow confidence intervals.

Thin-filament length correlates with fiber type in human skeletal muscle

Force production in skeletal muscle is proportional to the amount of overlap between the thin and thick filaments, which, in turn, depends on their lengths. Both thin- and thick-filament lengths are precisely regulated and uniform within a myofibril. While thick-filament lengths are essentially constant across muscles and species (∼1.65 μm), thin-filament lengths are highly variable both across species and across muscles of a single species. Here, we used a high-resolution immunofluorescence and image analysis technique (distributed deconvolution) to directly test the hypothesis that thin-filament lengths vary across human muscles. Using deltoid and pectoralis major muscle biopsies, we identified thin-filament lengths that ranged from 1.19 ± 0.08 to 1.37 ± 0.04 μm, based on tropomodulin localization with respect to the Z-line. Tropomodulin localized from 0.28 to 0.47 μm further from the Z-line than the NH(2)-terminus of nebulin in the various biopsies, indicating that human thin filaments have nebulin-free, pointed-end extensions that comprise up to 34% of total thin-filament length. Furthermore, thin-filament length was negatively correlated with the percentage of type 2X myosin heavy chain within the biopsy and shorter in type 2X myosin heavy chain-positive fibers, establishing the existence of a relationship between thin-filament lengths and fiber types in human muscle. Together, these data challenge the widely held assumption that human thin-filament lengths are constant. Our results also have broad relevance to musculoskeletal modeling, surgical reattachment of muscles, and orthopedic rehabilitation.

Genetic and biomechanical determinants of glenoid version: Implications for glenoid implant placement in shoulder arthroplasty

SUMMARY The universally accepted method of measuring glenoid version to determine proper alignment of the glenoid component during total shoulder arthroplasty does not account for the complex and variable relationship of the glenoid vault with the scapular body. Existing evidence indicates that the glenoid and the scapular body development are controlled by independent genetic and biomechanical factors. This raises the question: How relevant is the relationship of the glenoid face to the scapular body? This review paper integrates our present understanding of the genetics of scapular development and congenital and neuromuscular conditions to generate insights into scapular morphology and biomechanics. Glenoid version as traditionally defined may have limited relevance when positioning the glenoid component during total shoulder arthroplasty. Further studies of soft-tissue and muscular balance are needed to fully understand the consequences of variations in glenoid version. LEVEL OF EVIDENCE Review.

Posterior augmented glenoid designs preserve more bone in biconcave glenoids

BACKGROUND AND HYPOTHESIS Total shoulder arthroplasty is recommended treatment for severe osteoarthritis of the glenohumeral joint, which often results in excessive posterior wear. Two recent glenoid components with posterior augments have been designed to correct excessive posterior wear and retroversion. Our primary hypothesis was that posterior augmented glenoid designs require less bone removal than a standard glenoid design. METHODS Ten arthritic scapulae classified as Walch B2 glenoids were virtually implanted with standard, stepped, and wedged components. The volume of surgical bone removal, the maximum reaming depth, and the portion of the implant surface in contact with cancellous vs. cortical bone were calculated for each implant. RESULTS The neoglenoid made up an average of 65% ± 12% of the glenoid width. Mean surgical bone volume removed was least for the wedged (2857 ± 1618 mm(3)) compared with the stepped (4307 ± 1485 mm(3); P < .001) and standard (5385 ± 2348 mm(3); P < .001) designs. Maximum bone depth removed for the wedged (4.2 ± 2.0 mm) was less than for the stepped (7.6 ± 1.2 mm; P < .001) and standard (9.9 ± 3.2 mm; P < .001). The mean percentage of the implants back surface supported by cancellous bone was 18.2% for the standard, 8.8% for the stepped (P = .02), and 4.3% for the wedged (P = .01). DISCUSSION Both augmented components corrected glenoid version to neutral and required less bone removal, required less reaming depth, and were supported by more cortical bone than in the standard implant. The least amount of bone removed was with the wedged design.

Posterior augmented glenoid implants require less bone removal and generate lower stresses: a finite element analysis

HYPOTHESIS Glenoid retroversion can be corrected with standard glenoid implants after anterior-side asymmetric reaming or by using posterior augmented glenoid implants with built-in corrections. The purpose of this study was to compare 2 augmented glenoid designs with a standard glenoid design, measure the amount of bone removed, and compute the stresses generated in the cement and bone. METHODS Finite element models of 3 arthritic scapulae with varying severities of posterior glenoid wear were each implanted with 4 different implant configurations: standard glenoid implant in neutral alignment with asymmetric reaming, standard glenoid implant in retroversion, glenoid implant augmented with a posterior wedge in neutral alignment, and glenoid implant augmented with a posterior step in neutral alignment. The volume of cortical and cancellous bone removed and the percentage of implant back surface supported by cortical bone were measured. Stresses and strains in the implant, cement, and glenoid bone were computed. RESULTS Asymmetric reaming for the standard implant in neutral version required the most bone removal, resulted in the lowest percentage of back surface supported by cortical bone, and generated strain levels that risked damage to the most bone volume. The wedged implant removed less bone, had a significantly greater percentage of the back surface supported by cortical bone, and generated strain levels that risked damage to significantly less bone volume. CONCLUSIONS The wedged glenoid implants appear to have various advantages over the standard implant for the correction of retroversion. LEVEL OF EVIDENCE Basic Science Study; Computer Modeling.