Jason L. Koh

Efficacy of Surgical Preparation Solutions in Shoulder Surgery

BACKGROUND Deep infection following shoulder surgery is a rare but devastating problem. The use of an effective skin-preparation solution may be an important step in preventing infection. The purposes of the present study were to examine the native bacteria around the shoulder and to determine the efficacy of three different surgical skin-preparation solutions on the eradication of bacteria from the shoulder. METHODS A prospective study was undertaken to evaluate 150 consecutive patients undergoing shoulder surgery at one institution. Each shoulder was prepared with one of three randomly selected solutions: ChloraPrep (2% chlorhexidine gluconate and 70% isopropyl alcohol), DuraPrep (0.7% iodophor and 74% isopropyl alcohol), or povidone-iodine scrub and paint (0.75% iodine scrub and 1.0% iodine paint). Aerobic and anaerobic cultures were obtained prior to skin preparation for the first twenty patients, to determine the native bacteria around the shoulder, and following skin preparation for all patients. RESULTS Coagulase-negative Staphylococcus and Propionibacterium acnes were the most commonly isolated organisms prior to skin preparation. The overall rate of positive cultures was 31% in the povidone-iodine group, 19% in the DuraPrep group, and 7% in the ChloraPrep group. The positive culture rate for the ChloraPrep group was lower than that for the povidone-iodine group (p < 0.0001) and the DuraPrep group (p = 0.01). ChloraPrep and DuraPrep were more effective than povidone-iodine in eliminating coagulase-negative Staphylococcus from the shoulder region (p < 0.001 for both). No significant difference was detected among the agents in their ability to eliminate Propionibacterium acnes from the shoulder region. No infections occurred in any of the patients treated in this study at a minimum of ten months of follow-up. CONCLUSIONS ChloraPrep is more effective than DuraPrep and povidone-iodine at eliminating overall bacteria from the shoulder region. Both ChloraPrep and DuraPrep are more effective than povidone-iodine at eliminating coagulase-negative Staphylococcus from the shoulder.

The Effect of Graft Height Mismatch on Contact Pressure Following Osteochondral Grafting A Biomechanical Study

Hypothesis Incongruity of the articular cartilage following osteochondral transplantation affects surface contact pressure. Study Design An 80 N load was applied for 120 seconds to the femoral condyles of 10 swine knees. Contact pressures were measured using Fuji prescale film. Seven conditions were tested: (1) intact articular surface; (2) 4.5-mm diameter defect; (3) grafted with 4.5-mm diameter plug elevated 1 mm above adjacent cartilage; (4) plug elevated 0.5 mm; (5) plug flush; (6) plug sunk 0.5 mm below surface; and (7) sunk 1.0 mm. Conclusions Peak contact pressures were significantly (P< .001) elevated by ~20% after defect creation and were reduced to normal when plugs were flush. There were large and significant (P< .001) increases in pressure with plugs elevated 1 and 0.5 mm. Contact pressures with plugs sunk 0.5 and 1 mm were significantly (P< .01) higher than intact cartilage but were significantly (P < .01) lower than an empty defect. Clinical Relevance Normal contact pressures and patterns can be duplicated with flush articular surface grafts. However, small incongruities, particularly when the plug is elevated, can lead to significantly increased pressure. This reinforces the importance of articular surface congruity in the initial biomechanical state following osteochondral implantation.

In vivo noninvasive evaluation of abnormal patellar tracking during squatting in patients with patellofemoral pain

BACKGROUND Patellofemoral pain syndrome is one of the most common knee problems and may be related to abnormal patellar tracking. Our purpose was to compare, in vivo and noninvasively, the patellar tracking patterns in symptomatic patients with patellofemoral pain and those in healthy subjects during squatting. We tested the hypothesis that patients with patellofemoral pain exhibit characteristic patterns of patellar tracking that are different from those of healthy subjects. METHODS Three-dimensional patellar kinematics were recorded in vivo with use of a custom-molded patellar clamp and an optoelectronic motion capture system in ten healthy subjects and nine subjects with patellofemoral pain. The position of osseous knee landmarks was digitized while subjects stood upright, and then patellofemoral kinematics were recorded during squatting. The tracking technique was validated with use of both in vitro and in vivo methodologies, and the average absolute error was <1.2 degrees and <1.1 mm. RESULTS At 90 degrees of knee flexion, the patella showed lateral spin (the distal pole of the patella rotated laterally) in subjects with patellofemoral pain (mean and standard deviation, -10.13 degrees +/- 2.24 degrees) and medial spin in healthy subjects (mean, 4.71 degrees +/- 1.17 degrees) (p < 0.001). At 90 degrees of knee flexion, the patella demonstrated significantly more lateral translation in subjects with patellofemoral pain (mean, 5.05 +/- 3.73 mm) than in healthy subjects (mean, -4.93 +/- 3.93 mm) (p < 0.001). CONCLUSIONS Kinematic differences between healthy subjects and subjects with patellofemoral pain were demonstrated through a large, dynamic range of knee flexion angles. Increased lateral patellar translation and lateral patellar spin in subjects with patellofemoral pain suggest that the patella is not adequately balanced during functional activities in this group. Prospective studies are needed to identify when patellofemoral pain-related changes begin to occur and to determine the risk for the development of patellofemoral pain in individuals with abnormal kinematics.

GROWTH AND DIFFERENTIATION FACTORS FOR CARTILAGE HEALING AND REPAIR

Chondrocyte differentiation and the maintenance of function requires both transient and long-lasting control through humoral factors, particularly under stress, repair and regeneration in vivo or in vitro as in cell and tissue culture. To date, humoral factors from all major classes of molecules are known to contribute: ions (calcium), steroids (estrogens), terpenoids (retinoic acid), peptides (PTHRP, PTH, insulin, FGFs) and complex proteins (IGF-1, BMPs). They may act indirectly through membrane receptors and signal pathways or directly on transcriptional control elements. Those molecules may reach chondrocytes via free diffusion or may be bound to collagens or proteoglycans on extracellular matrix superstructures becoming available on metabolic processing of collagens and/or proteoglycans. Depending on their position in the metabolic cascade controlling chondrocyte development and homeostasis, they may be used in tissue engineering and regenerative approaches towards cartilage repair by direct application, carrier-mediated release or genetic delivery.

Supplementation of Rotator Cuff Repair with a Bioresorbable Scaffold

Background Repair of a torn rotator cuff should have sufficient initial strength of the fixation to permit appropriate rehabilitation. Hypothesis Augmentation with a woven polylactic acid scaffold strengthens repairs of the rotator cuff. Study Design Controlled laboratory study. Methods In the suture-anchor model, 10 pairs of sheep infraspinatus tendons were detached and repaired to suture anchors. In half of the matched specimens, the repair was reinforced with a woven poly-lactic acid scaffold repaired with the tendon to bone. In the bone-bridge model, sutures were passed through a trough and over a bone bridge distal to the greater tuberosity; half were reinforced by the scaffold. The repairs were tested to failure with a hydraulic testing machine. Results The mean ultimate strength of suture-anchor repairs augmented with the scaffold (167.3 ± 53.9 N) was significantly greater than that of nonaugmented fixation (133.2 ± 38.2 N). Failure occurred when the tendon pulled through the sutures; the scaffold remained intact. Scaffold reinforcement of the bone bridge significantly increased the ultimate strength from 374.6 ± 117.6 N to 480.9 ± 89.2 N, and the scaffold remained intact in 8 of 10 specimens. Conclusions The scaffold significantly increased the initial strength of rotator cuff repair by approximately 25%.

Bone density adjacent to press-fit acetabular components. A prospective analysis with quantitative computed tomography.

Background: The status of periprosthetic bone stock is an important concern when revision total hip arthroplasty is undertaken. Remodeling of periprosthetic femoral bone after total hip arthroplasty has been studied extensively, and the phenomenon of femoral stress-shielding has been well characterized. Finite element analysis and computer-simulated remodeling theory have predicted that retroacetabular bone-mineral density decreases after total hip arthroplasty; however, remodeling of periprosthetic pelvic bone in this setting has yet to be well defined. This study was conducted to evaluate the short-term natural history of periacetabular bone-mineral density following primary total hip arthroplasty. Methods: Periacetabular bone-mineral density was studied prospectively in a group of twenty-six patients who underwent primary hybrid total hip arthroplasty for the treatment of advanced osteoarthritis. Density within the central part of the ilium (directly cephalad to a press-fit acetabular component) was assessed with serial quantitative computed tomography. Baseline density was measured within the first five days following the total hip arthroplasty. Ipsilateral density measurements were repeated at an average of 1.28 years postoperatively. Density values at corresponding levels of the contralateral ilium were obtained at both time-points in all patients to serve as internal controls. Results: Bone-mineral density decreased significantly (p £ 0.001) between the two time-points on the side of the operation. The mean absolute magnitude of the interval density reduction (75 mg/cc) was greatest immediately adjacent to the implant (p < 0.001), but it was also significantly reduced (by 35 mg/cc) at a distance of 10 mm cephalad to the implant (p = 0.001). Relative declines in mean density ranged from 33% to 20% of the baseline values. No focal bone resorption (osteolysis) was detected at the time of this short-term follow-up study. With the numbers available, no significant interval alteration in bone-mineral density was found on the untreated (internal control) side (p 0.07). Conclusions: We suggest that the observed decline in bone-mineral density represents a remodeling response to an altered stress pattern within the pelvis that was induced by the presence of the acetabular implant. This finding corroborates the predictions of finite element analysis and computer-simulated remodeling theory. It remains to be seen whether this trend of atrophy of retroacetabular bone stock will continue with longer follow-up or will ultimately affect the long-term stability of press-fit acetabular components.

The Effect of Angled Osteochondral Grafting on Contact Pressure A Biomechanical Study

Background Flush osteochondral plugs can reduce contact pressure compared with an empty defect in the articular cartilage. However, incongruities such as graft angulation have an unknown effect. Hypothesis Incongruity of the articular cartilage after osteochondral transplantation affects articular surface contact pressure. Study Design Controlled laboratory study. Methods An 80-N load was applied with a material testing system for 120 seconds to the femoral condyles of 50 fresh swine knees. Contact pressures were measured using Prescale super low film. Five conditions were tested: (1) intact articular surface; (2) surface with 4.5-mm-diameter circular defect; (3) defect grafted with a flush 4.5-mm-diameter plug from the contralateral condyle; (4) defect grafted with a 30 ° angled 4.5-mm-diameter plug, with lower edge flush (tip elevated with respect to the adjacent surface); and (5) defect grafted with a 30 ° plug, with tip flush to the adjacent surface (lower edge sunk). Angled grafts were obtained using a rotational bearing vise aligned with a 30 ° fixed-angle track. The film was digitally scanned and analyzed, and standard statistical tests were performed. Results Mean peak pressures of intact cartilage (8.57 kg/cm2), flush graft (9.81 kg/cm2), and sunk and angled graft (9.15 kg/cm2) were not significantly different (P <. 5). The mean pressures for defects (12.01 kg/cm2) and the elevated angled graft (14.50 kg/cm2) were significantly (P <. 05) higher than that of intact cartilage. Clinical Relevance Slightly sunk grafts were still able to reduce elevated contact pressures to normal levels. However, elevated angled grafts increased contact pressure. These results suggest that it is preferable to leave an edge slightly sunk rather than elevated.

In vivo load sharing among the quadriceps components

Knee extension is always performed with coordinated contractions of multiple quadriceps muscle components: however, how the load is shared among them under normal and pathological conditions is unclear. We hypothesized that: the absolute moment generated by each quadriceps component increases with the total knee extension moment; the relative contribution and its dependence on the total knee extension moment are different for different quadriceps components; and the centrally located large vastus intermedius (VI) is favored by the central nervous system at low levels of activation. Electrical stimulation was used to activate each quadriceps component selectively in six human subjects. The relationship between the knee extension moment generated by an individual quadriceps component and the corresponding compound muscular action potential (M‐wave) over various contraction levels was established for each quadriceps component. This relationship was used to calibrate the corresponding EMG signal and determine load sharing among quadriceps components during submaximal isometric voluntary knee extension. The VI contributed the most (51.8–39.6%) and vastus medialis the least (9.5–12.2%) to knee extension moment (P < 0.05). As the knee extension moment increased, the relative contribution of the VI decreased (P = 0.017) while the relation contribution of the vastus lateralis and medialis increased (P ≤ 0.012). The absolute moment generated by each quadriceps component always increased with the total knee extension moment (P < 0.002). Our in vivo approach determined subject‐ and condition‐specific load sharing among individual muscles and showed that the central nervous system utilized the centrally located, uniarticular VI in submaximal isometric knee extension.

In vivo and Noninvasive Three-Dimensional Patellar Tracking Induced by Individual Heads of Quadriceps

PURPOSE Unbalanced actions of the quadriceps components are closely linked to patellar mal-tracking and patellofemoral pain syndrome. However, it is not clear how individual quadriceps components pull and rotate the patella three dimensionally. The purpose of this study was to investigate in vivo and noninvasively patellar tracking induced by individual quadriceps components. METHODS Individual quadriceps component was activated selectively through electrical stimulation at the muscle motor point, and the resulting patellar tracking was measured in vivo and noninvasively in 18 knees of 12 subjects. The in vivo and noninvasively patellar tracking was corroborated with in vivo fluoroscopy and in vitro cadaver measurements. RESULTS Vastus medialis (VM) mainly pulled the patella first in the medial and second in the proximal directions and vastus lateralis (VL) pulled first in the proximal and second in the lateral directions. The oblique portion (VMO) of the VM pulled the patella mainly medially and the longus portion (VML) more proximally. Medial tilt was the major patellar rotation induced by VMO contraction at full knee extension. With the knee at the more flexed positions, the amplitude of patellar movement induced by comparable quadriceps contractions was reduced significantly compared to that at full knee extension, and VMO changed its main action from extending to flexing the patella. CONCLUSIONS The medial and lateral quadriceps components moved the patella in rather different directions, and rotated the patella differently about the mediolateral tilt and mediolateral rotation axes but similarly in extension. The approach can be used to investigate patellar tracking in vivo and noninvasively in both healthy subjects and patients with patellofemoral disorder and patellar malalignment.

Biomechanical and histological evaluation of osteochondral transplantation in a rabbit model.

Background Biomechanical and histological properties of osteochondral transplantation have not been extensively examined. Hypothesis Osteochondral grafts have properties similar to native articular cartilage. Study Design Controlled laboratory study. Methods A 2.7 mm (diameter) × 4.0 mm (depth) osteochondral defect was created in 17 New Zealand white rabbit knees. An osteochondral graft, harvested from the contralateral knee, was transplanted into the defect. Eight rabbits were sacrificed each at 6 and 8 weeks. Results The 12-week grafts (1213.6 ± 309.0 N/mm) had significantly higher stiffness than the 6-week grafts (483.1 ± 229.1 N/mm; P< .001) and of normal cartilage (774.8 ± 117.1 N/mm; P< .003). Stiffness of the 6-week grafts was significantly lower than normal cartilage (P< .036). At all time points, full-thickness defects had significantly lower stiffness than normal cartilage (P< .001). Histologically, transplanted grafts scored significantly higher than the full-thickness defects (P< .001). The defects showed inconsistent, fibrocartilage healing. The grafts demonstrated cartilage viability, yet with a persistent cleft between the graft and host. Conclusions Osteochondral transplants undergo increased stiffness in the short term, with evidence of structurally intact grafts. Clinical Relevance Osteochondral transplantation may be a viable treatment option; however, long-term investigation on graft function is necessary.