Peter Simon

In vivo topographic analysis of lumbar facet joint space width distribution in healthy and symptomatic subjects.

Study Design. In vivo 3-dimensional facet joint space width measurement. Objective. To determine lumbar facet joint space width within clinically relevant topographical zones in vivo and its correlations with age, level, and presence of lower back pain symptoms. Summary of Background Data. Facet joint gap narrowing, articular cartilage thinning, and subarticular cortical bone hypertrophy are frequently observed age-related changes. Facet joint space width is a well-defined parameter to evaluate osteoarthritis. To the best of our knowledge, there is no other study that quantifies 3-dimensional facet joint space width distribution in vivo. Methods. Three-dimensional measurement to quantify facet joint space width distribution based on 5 clinically relevant topographic zones in a cohort of healthy and symptomatic volunteers with low back pain, using subject-based 3-dimensional computed tomographic models with respect to spinal level, subject age, sex, and presence/absence of lower back pain. Results. Facet joint space width (mean ± SD) was 1.93 ± 0.51 mm for the central zone, 1.75 ± 0.48 mm for the superior zone, 1.63 ± 0.49 mm for the inferior zone, 1.48 ± 0.44 mm for the medial zone, and 1.65 ± 0.48 mm for the lateral zone, respectively. There were no significant differences between right and left facet joints. Male patients showed larger space width than female patients. Overall, space width of symptomatic subjects was significantly narrower than that of the asymptomatic group. Facet joints in the peripheral zones were narrower than in the central zone. Age-group comparisons showed that local narrowing occurring as early as in the third decade at the inferior zone of L5–S1, with all the remaining zones implicated after the fourth decade. Conclusion. This in vivo study shows variations in facet joint space width narrowing with spinal level and region within the facet joint and in vivo evidence of localized, age-influenced facet cartilage thinning. Techniques developed in this study may be applied in the detection of early osteoarthritis-related changes in the facet joints.

Glenoid subchondral bone density distribution in male total shoulder arthroplasty subjects with eccentric and concentric wear

BACKGROUND Glenoid component loosening in total shoulder arthroplasty may be prevented by component placement on a congruent and adequate bony surface. Glenoid subchondral bone density (SBD) variability may be correlated with this concept. This study analyzed the 3-dimensional distribution of glenoid SBD in total shoulder arthroplasty patients with osteoarthritis. MATERIALS AND METHODS Three-dimensional computed tomography osteoabsorptiometry (CT-OAM) was performed in 42 men (21 with eccentric and 21 with concentric wear patterns) with glenohumeral arthritis. Glenoid SBD was measured from the joint surface based on 5 clinically relevant topographic zones. The correlation of the wear pattern with the SBD distribution was investigated. RESULTS The glenoid subarticular layers could be separated into distinct regions: calcified cartilage (≤ 1.5 mm), subchondral plate (2-4.5 mm) and cancellous bone (≥ 5 mm). There were significant differences in SBD among these layers within and between patients with concentric and eccentric wear patterns. In concentric glenoids, the SBD distribution was homogeneous, with greater mineralization in the central zone, 1,749.1 ± 162.3 Hounsfield units (HU) (at 2.5 mm), compared with the posterior, anterior, and superior zones (P < .001). In the eccentric group, the SBD distribution was inhomogeneous. Mineralization was greatest in the posterior zone, 1,739.0 ± 172.6 HU (at 2.5 mm), followed by the inferior zone, 1,722.1 ± 186.6 HU (at 3 mm). CONCLUSION This study represents the first study using CT-OAM to evaluate the 3-dimensional SBD distribution of the glenoid vault for different arthritic wear patterns. The study findings indicate that the SBD distribution is dependent on (1) depth from the articular surface, (2) topographic zone, and (3) wear pattern. CT-OAM may be an effective tool to assist in preoperative planning for shoulder arthroplasty.

Revision for a failed reverse: a 12-year review of a lateralized implant.

BACKGROUND The purpose of this study was (1) to evaluate the rates of reverse shoulder arthroplasty (RSA) revisions during a 12-year period, (2) to assess the influence of primary diagnosis and the impact of implant modifications on revisions, (3) to describe surgical management of failed RSA, and (4) to analyze outcomes of patients with minimum 24-month follow-up. METHODS A retrospective database review identified primary diagnosis for 1418 patients who underwent RSA from 2000 to 2012. A subgroup of 85 patients required return to the operating room for removal or exchange of components. Indication to reoperate, intraoperative management, and outcomes were reviewed. Indications were grouped into 7 categories: baseplate failure, humeral component dissociation, glenosphere dissociation, glenohumeral dislocation, aseptic humeral loosening, periprosthetic fracture, and infection. During the study, design modifications were made to the baseplate, humeral socket, and glenosphere. Surgical strategies were analyzed through operative reports. Range of motion, American Shoulder and Elbow Surgeons scores, and Simple Shoulder Test scores were collected before and after surgery and compared for 58 patients with 2-year follow-up. RESULTS Overall revision rate was 6%. Patients undergoing RSA for failed hemiarthroplasty had the highest revision rate (10%). Indications for revision included baseplate failure (2.5%), infection (1.3%), humeral dissociation (0.7%), glenosphere dissociation (0.6%), periprosthetic fracture (0.4%), glenohumeral dislocation (0.4%), and aseptic humeral loosening (0.3%). Baseplate modifications reduced the incidence of baseplate failure to 0.3%. Range of motion and the Simple Shoulder Test and American Shoulder and Elbow Surgeons scores improved. CONCLUSION Although revision RSA is challenging, with higher risk for complications compared with primary RSA, patients still exhibit significant clinical improvements.

Biomechanical comparison of occiput-C1-C2 fixation techniques: C0-C1 transarticular screw and direct occiput condyle screw

Study Design. In vitro human cadaveric biomechanical study. Objective. The objective was to evaluate and compare the construct stability of occiput-C1–C2 fixation provided by C0–C1 transarticular screws or occipital condyle screws. Summary of Background Data. The placement of an occipital plate is commonly recommended in occipitocervical fixation surgery. However, there are unique clinical situations in which the placement of the occipital plate may not be possible or may have already failed. For these situations, 2 novel techniques that use the occipital condyle have been recently introduced: (1) C0–C1 transarticular screws fixation and (2) direct occipital condyle screws and C1 lateral mass screws fixation. However, there is a lack of thorough biomechanics studies of these techniques. Methods. Nondestructive kinematic tests and destructive tests were conducted in 16 fresh frozen cadaveric spines. As a nondestructive kinematic test, a pure moment of up to 2.0 N·m was applied in smooth continuous flexion/extension, lateral bending, and axial rotation motions. In addition to an intact-state case, a total of 5 different constructs (standard occipital plate, C0–C1 transarticular screws with/without occipital plate, and occipital condyle screws with/without occipital plate) were tested after destabilization of C0–C1 and C1–C2. All constructs had C2 pedicle screws fixation, and occipital condyle screws were incorporated with C1 lateral screws. Results. All fixation techniques significantly reduced ranges of motion compared with the intact state. In comparison with the standard occipital plate construct, the 2 novel techniques showed higher stability in axial rotation and lower stability in lateral bending. In both nondestructive and destructive tests, there were no statistical differences between C0–C1 transarticular screw construct and occipital condyle screw construct. Conclusion. The C0–C1 transarticular screw technique and direct occipital condyle screw with C1 lateral mass screw technique can be salvage fixation methods when occipital plate fixation is not feasible.

Biomechanical effect of the C2 laminar decortication on the stability of C2 intralaminar screw construct and biomechanical comparison of C2 intralaminar screw and C2 pars screw.

BACKGROUND: There have been no reports of biomechanical stability of C1-2 constructs after decortication of the C2 lamina. In addition, few studies have compared the stability of C2 laminar screw and pars screw constructs. OBJECTIVE: To compare the biomechanical stability of 3 different C1-2 construct conditions (C2 pars screw, C2 intralaminar screw, C2 intralaminar construct with C2 laminar decortication). METHODS: Fourteen fresh-frozen cadaveric cervical specimens (C1-3) were used. In 7 specimens, pure moments of 1.5 Nm were applied in flexion/extension, lateral bending, and axial rotation. Each specimen was tested in the normal state, in the destabilized state (after odontoidectomy and resection of transverse atlantal ligament), and after application of constructs. After kinematic study, these 7 specimens underwent axial pullout strength testing of pars screw and 50% decorticated C2 intralaminar screws. In another 7 specimens, insertion torque and pullout strength were measured to compare the pars screw and intact C2 intralaminar screw. RESULTS: There were no statistically significant differences between the intact C2 intralaminar and 50% decorticated C2 intralaminar screw constructs in terms of range-of-motion limitations. The C2 pars screw construct was significantly superior to the C2 laminar screw construct in lateral bending (P < .01) and axial rotation (P < .01) and equivalent to the C2 laminar screw construct in flexion/extension (P = .42). There was no significant pullout strength difference between the 3 kinds of C2 screw. CONCLUSION: The C1 lateral mass-C2 pars screws construct was stronger than the C1 lateral mass-C2 intralaminar screw construct. Decortication of C2 laminar (up to 50%) did not affect the immediate stability of the C1-2 construct.

Surgical management of periprosthetic shoulder infections

BACKGROUND The treatment of periprosthetic joint infection is a difficult challenge in shoulder arthroplasty. This study investigated 1-stage modular component exchange vs. 1-stage complete removal and reimplantation (CRR) vs. 2-stage revision arthroplasty for periprosthetic joint infection. METHODS Between January 1, 2004, and December 31, 2012, 79 patients received a component exchange (n = 15), CRR (n = 45), or a 2-stage (n = 19) revision for infection. A binary logistic regression analysis was performed to determine factors presenting the greatest risk of reinfection. Complications and functional outcomes were also evaluated. RESULTS Overall, 4 of 15 (27%) component exchanges, 2 of 45 (4%) CRRs, and 4 of 19 (21%) 2-stage procedures required a reoperation for infection with a minimum of 1 year of follow-up. The difference between the CRR group and exchange group was significant (P = .030); however, the difference between the CRR group and 2-stage group did not reach statistical significance (P = .059). No preoperative and intraoperative selection bias between the groups was found. Binary logistic regression predicted that reinfection was highest in patients whose cultures grew Staphylococcus aureus (P = .004) or coagulase-negative Staphylococcus species (P = .041) or those treated with a component exchange (P = .015). The difference between groups for noninfection-related complications was not significant (P = .703). All procedures provided improved functional outcomes and pain relief. CONCLUSION Patients with infection caused by Staphylococcus aureus or coagulase-negative Staphylococcus species may require additional operations to treat the infection. Although effective in some cases, component exchange presents an increased risk for reinfection. A 1-stage CRR procedure had similar reinfection rates as a 2-stage procedure in our patient population.

Classification of instability after reverse shoulder arthroplasty guides surgical management and outcomes

BACKGROUND Revision of unstable reverse shoulder arthroplasty (RSA) remains a significant challenge. The purpose of this study was to determine the reliability of a new treatment-guiding classification for instability after RSA, to describe the clinical outcomes of patients stabilized operatively, and to identify those with higher risk of recurrence. METHODS All patients undergoing revision for instability after RSA were identified at our institution. Demographic, clinical, radiographic, and intraoperative data were collected. A classification was developed using all identified causes of instability after RSA and allocating them to 1 of 3 defined treatment-guiding categories. Eight surgeons reviewed all data and applied the classification scheme to each case. Interobserver and intraobserver reliability was used to evaluate the classification scheme. Preoperative clinical outcomes were compared with final follow-up in stabilized shoulders. RESULTS Forty-three revision cases in 34 patients met the inclusion for study. Five patients remained unstable after revision. Persistent instability most commonly occurred in persistent deltoid dysfunction and postoperative acromial fractures but also in 1 case of soft tissue impingement. Twenty-one patients remained stable at minimum 2 years of follow-up and had significant improvement of clinical outcome scores and range of motion. Reliability of the classification scheme showed substantial and almost perfect interobserver and intraobserver agreement among all the participants (κ = 0.699 and κ = 0.851, respectively). DISCUSSION Instability after RSA can be successfully treated with revision surgery using the reliable treatment-guiding classification scheme presented herein. However, more understanding is needed for patients with greater risk of recurrent instability after revision surgery.

The influence of patient- and surgeon-specific factors on operative duration and early postoperative outcomes in shoulder arthroplasty

BACKGROUND Increased operative duration has been shown to have demonstrable effects on the outcomes and complications in multiple areas of orthopedic surgery. We sought to determine if patient- and surgeon-specific factors correlated to operative duration in shoulder arthroplasty. Our hypothesis was that increased surgeon and trainee volume would decrease operative times and that more complex pathology would increase operative duration. METHODS A retrospective review of primary and revision total and reverse shoulder arthroplasties performed at a single institution from 2012 through 2015 was performed evaluating the correlation between specific patient and surgeon factors and operative duration. The influence of operative duration on postoperative length of stay and risk of readmission within 30 days was also analyzed. RESULTS For surgeon-specific factors, high surgeon volume (>30 shoulder arthroplasties/year) was associated with shorter operative duration (105.9 vs. 128.3 minutes; P < .001). Progression through the fellowship academic year was found to be associated with decreased surgical times (100.7 vs. 116.5 minutes; P < .0001). Certain complex pathologic processes (reverse shoulder arthroplasty for sequelae of prior fracture, total shoulder arthroplasty for dysplastic glenoid morphology, revision surgery) showed increased operative times. Patients with postoperative readmission had a longer mean operative time (163 vs. 107.1 minutes). CONCLUSIONS Increased surgeon and trainee volumes were associated with decreased operative duration in shoulder arthroplasty. Patients with more complex pathology were more likely to have increased surgical times. Postoperative readmission within 30 days was associated with increased operative duration. Consideration of patient selection by surgeons to minimize operative times may reduce readmissions.

Biomechanics of the Clavicle

The clavicle is an S-shaped bone that acts as the only osseous link between the upper extremity skeleton and the thorax. It serves as a solid strut to position the upper limb away from the trunk and enhance more global positioning and use of the limb. When this strut is fractured and either left untreated or not repaired adequately, clavicular malunion can occur. The subsequent shortening of the clavicle decreases the moment-generating capacity of the upper extremity and results in impaired mobility. Preserving the length and anatomy of the clavicle is therefore very important in maintaining optimal function of the upper extremity. This chapter should help the surgeon be more cognizant of the clavicle biomechanics involved during arm motion and will hopefully help to guide the surgeon in the type of implant they should use.

Non-Contact Experimental Assessment of Spinal Facet Joint Cartilage Dehydration

Dehydration may cause undesirable morphological changes in small hydrated tissue with high surface-to-volume ratio during in vitro experimentation that can result in erroneous data. The lumbar facet joint cartilage, an example of such tissue, is highly susceptible to dehydration due its high content of water (60% to 80% by volume) when exposed to ambient air [1]. Recent studies involving thickness measurement of articular human and bovine cartilage from the tibial plateau reported distinct decreases in thickness due to dehydration and the importance of maintaining its hydration during biomechanical experimental studies [1–3]. Knee joint and facet joint cartilage are characterized as hyaline cartilage surrounded by synovial fluid and encased in a joint capsule. The fact that both are synovial joints suggests that facet joint cartilage may show similar dehydration rates; however, due to its smaller size and different surface-to-volume, the dehydration rate is expected to be higher for facet joint cartilage. To the best of the authors’ knowledge, the rate of facet joint cartilage dehydration has not been quantified before. It is hypothesized that the facet joint cartilage thickness will decrease in an inverse exponential trend and significant changes will be seen as dehydration time intervals time increases. The objectives of this study were: 1) quantify the dimensional stability of the cartilage samples under a sequential dehydration protocol, and 2) to evaluate the cartilage shrinkage rate.Copyright