Thomas R. Gardner

Mechanical Properties of Soft Tissue Femoral Fixation Devices for Anterior Cruciate Ligament Reconstruction

Purpose To evaluate femoral soft tissue fixation for anterior cruciate ligament reconstruction. Hypothesis Femoral fixation devices have different ultimate strengths and slippage under cyclic loading. Study Design Controlled laboratory study. Methods Thirty-three porcine femora were used to study interference screw (9), Endobutton (8), Rigidfix cross-pin (8), and Bio-Transfix cross-pin (8) fixation methods. Fixation slippage was evaluated under cyclical load from 50 N to 250 N using a materials testing machine. Ultimate load was determined with a single load to failure. Results Total graft slippage was greater (P< .001) for the Rigidfix (6.02 ± 2.12 mm) and the interference screw (5.44 ± 3.25 mm) compared to the Endobutton (1.75 ± 0.97 mm) and the Bio-Transfix (1.14 ± 0.53 mm). All techniques showed the greatest slippage during the first 100 cycles (Rigidfix 84%, Endobutton 70%, interference screw 56%, and Bio-Transfix 55%). The failure load for the interference screw technique (539 ± 114 N) was lower (P= .0008) than for the other 3 techniques (737 ± 140 N for Rigidfix, 746 ± 119 N for Bio-Transfix, and 864 ± 164 N for Endobutton). Conclusions The interference screw and the Rigidfix fixation demonstrated inferior fixation biomechanics compared to the Bio-Transfix and the Endobutton techniques.

Differences in patellofemoral joint cartilage material properties and their significance to the etiology of cartilage surface fibrillation

OBJECTIVE To determine if differences in biomechanical properties and biochemical composition exist between human patellar articular cartilage and the opposing femoral articular cartilage. DESIGN The biomechanical properties and biochemical composition of the articular cartilage of 17 knees from 13 donors were determined for four sites on the patella and three sites on the femur representing regions of contact at 30 degrees and 90 degrees of flexion. The material properties were determined by biphasic indentation testing, yielding the compressive aggregate modulus, HA, permeability, k, and Poissons ratio, vs. The thickness of the cartilage at the indentation site, h, was also measured using a needle probe. Full-thickness samples of cartilage adjacent to each indentation site were used for wet weight, sulfated glycosaminoglycan content and hydroxyproline content determinations. RESULTS The patellar cartilage was found to have a lower compressive aggregate modulus by 30% (P < 0.001), higher permeability to fluid flow by 66% (P < 0.001) and greater thickness by 23% (P = 0.017) than that of the opposing femoral cartilage. The Poissons ratios for both surfaces were found to be nearly zero. The water content of the patella was higher by 5% (P = 0.031) and the proteoglycan content lower by 19% (P = 0.030) than that of the femur. However, no differences were found between the collagen contents of the cartilages. CONCLUSIONS Significant differences were found between the intrinsic material properties of the patellar cartilage and those of the femoral-trochlear cartilage. This variability of cartilage material properties with the patellofemoral joint may help explain why patellar cartilage has been frequently observed clinically to exhibit earlier and more severe fibrillation changes than the opposing femoral cartilage.

Effect of Gender and Maturity on Quadriceps-to-Hamstring Strength Ratio and Anterior Cruciate Ligament Laxity:

Background Exercise programs have been introduced to reduce the ACL injury risk in female athletes. The most effective age at which to start these programs is not known. Hypothesis Age and gender affect ligament laxity and quadriceps-to-hamstring strength ratio. Study Design Cross-sectional study; Level of evidence, 3. Methods Fifty-three female and 70 male recreational soccer players, 10 to 18 years of age, were studied with physical examination, KT-1000 arthrometry, and manual maximum quadriceps and hamstring strength using a handheld dynamometer. The subjects were separated into 4 groups to examine maturity-related intergender differences: group G1, premenarchal girls (n = 24); group B1, boys 13 years and younger (n = 38); group G2, girls 2 or more years after menarche (n = 29); and group B2, boys 14 years and older (n = 32). Results Both knees of 123 soccer players were evaluated. The mean ages for groups G1, B1, G2, and B2 were 11.50 ± 1.69, 10.63 ± 1.85, 15.5 ± 1.43, and 15.59 ± 1.24 years, respectively, and the mean laxity measurements were 8.84 ± 2.12, 8.51 ± 1.61, 8.85 ± 1.86, and 7.33 ± 1.27 mm, respectively. Laxity was significantly less for the mature boys (P= .0015) than for the immature boys, mature girls, and immature girls. With increasing maturity, significant increases in both quadriceps and hamstring muscle strength were observed for both boys and girls (P< .05). Boys demonstrated a greater percentage increase in hamstring strength with maturity (179%) compared with girls (27%) (P< .05). Mature girls (2.06) had significantly greater quadriceps-tohamstring ratio when compared with immature girls (1.74), immature boys (1.58), and mature boys (1.48) (P< .05). Conclusion Female athletes after menarche increase their quadriceps strength greater than their hamstring strength, putting them at risk for anterior cruciate ligament injury. Anterior cruciate ligament–prevention programs based on improving dynamic control of the knee by emphasizing hamstring strengthening should be instituted for girls after menarche.

Simulation of surgical glenoid resurfacing using three-dimensional computed tomography of the arthritic glenohumeral joint: The amount of glenoid retroversion that can be corrected

HYPOTHESIS The magnitude of glenoid retroversion that can be surgically corrected in total shoulder arthroplasty and still enable implantation of a glenoid component has not been established. We hypothesized that increased retroversion will require smaller glenoid components for successful implantation when the glenoid is surgically corrected and that correction beyond 20 degrees of retroversion is not feasible without peg penetration. METHODS Using 3-dimensional models created from computed tomography of 19 patients with advanced shoulder osteoarthritis, we simulated glenoid resurfacing on varying degrees of retroverted, osteoarthritic glenoids using an in-line 3-peg glenoid component and asymmetric reaming to correct version. RESULTS Glenoids with preoperative retroversion of less than 12 degrees could always be implanted with 46-mm and 52-mm glenoid components at neutral version without vault violation. Conversely, glenoids with greater than 18 degrees of preoperative retroversion could not be implanted at neutral version due to vault violation from the pegs. The average preoperative glenoid retroversion of patients in which a 46-mm glenoid was implanted at neutral version was 8.9 degrees +/- 6.4 degrees compared with 19.0 degrees +/- 7.1 degrees for those that could not be implanted at neutral (P = .005). DISCUSSION Computer-aided surgical simulation shows that glenoid retroversion is a critical factor in determining successful glenoid implantation. Smaller sized glenoid components allow for greater version correction and less residual postsimulation retroversion when an in-line pegged component is used.

The Effect of Lifelong Exercise on Canine Articular Cartilage

The effect of long-term exercise on canine knees was studied to determine whether an increased level of lifelong weightbearing exercise causes degeneration, or changes that may lead to degeneration, of articular cartilage. Eleven dogs were exercised on a treadmill at 3 km/hr for 75 minutes 5 days a week for 527 weeks while carrying jackets weighing 130% of their body weight. Ten control dogs were allowed unrestricted activity in cages for the 550 weeks. At the completion of the study all knee joints were inspected for evidence of joint injury and degeneration. Articular cartilage sur faces from the medial tibial plateau were examined by light microscopy, the cartilage thickness was meas ured, and the intrinsic material properties were deter mined by mechanical testing. No joints had ligament or meniscal injuries, cartilage erosions, or osteophytes. Light microscopy did not demonstrate cartilage fibrilla tion or differences in safranin O staining of the tibial articular cartilages between the two groups. Further more, the tibial articular cartilage thickness and me chanical properties did not differ between the two groups. These results show that a lifetime of regular weightbearing exercise in dogs with normal joints did not cause alterations in the structure and mechanical properties of articular cartilage that might lead to joint degeneration.

Codominance of the Individual Posterior Cruciate Ligament Bundles An Analysis of Bundle Lengths and Orientation

Background: It is unclear how each bundle of the posterior cruciate ligament contributes to posterior knee stability. Hypothesis: Changes in bundle orientation and length occur such that neither bundle dominates in restraining posterior tibial motion throughout knee flexion and extension. Study Design: Controlled laboratory study. Methods: Six fresh-frozen cadaveric knees were studied in a joint-testing rig with individual quadriceps and hamstring muscle loading. Kinematic data for the tibia and femur were obtained at knee flexion angles from 0° to 120°. The joint was then disarticulated, and the insertions of the two bundles on the tibia and femur were digitized. Results: Length of the anterolateral bundle increased with increasing knee flexion angle from 10° to 120°. Length of the posteromedial bundle decreased with increasing knee flexion angle from 0° to 45° and increased slightly from 60° to 120°. Length of the anteromedial bundle was significantly less than that of the posteromedial at 0°, 10°, and 20° of knee flexion. The anterolateral bundle was significantly more horizontal at flexion angles of 0°, 10°, 20°, 30°, and 45° (P < 0.05). The posteromedial bundle was more horizontal at 120°. Conclusions: Changes in orientation take place such that neither bundle dominates in restraining posterior tibial motion throughout knee flexion and extension. Clinical Relevance: Double-bundle reconstructions achieve more physiologic knee function.

Investigation of the Preservation of the Fluid Seal Effect in the Repaired, Partially Resected, and Reconstructed Acetabular Labrum in a Cadaveric Hip Model

Background: Debate exists on whether hip labral tears should be surgically repaired, partially resected, or reconstructed. Furthermore, limited data exist regarding the fluid seal properties of hip labrum repair and/or reconstruction with iliotibial band autograft when compared with the labrum-intact condition. Hypothesis/Purpose: The purpose of this study was to investigate the fluid seal properties of hip labral repair and reconstruction techniques. We hypothesized that hip labral repair preserves the acetabular labral fluid seal greater than labral tear, partial-resection, and reconstruction conditions. Study Design: Controlled laboratory study. Methods: Six human cadaveric hemipelvises were dissected of all soft tissue, leaving the hip capsule intact. Fluid efflux was measured under 5 conditions using a custom fluid infusion device: (1) hip labrum intact, (2) labral tear, (3) labral repair with suture anchors, (4) partial labral resection, and (5) labral reconstruction using ipsilateral iliotibial band autograft. Joint fluid expression was measured as flow rate under 3 different pressure settings (2, 3, and 4 psi). Statistical differences between conditions were assessed using 2-way, repeated-measures analysis of variance. The Student-Newman-Keuls (SNK) multiple comparison test was used to determine differences between levels. Results: There was a significant increase in fluid efflux with a simulated labral tear (0.54 ± 0.3 mL/sec) when compared with the intact hip labrum condition (0.006 ± 0.008 mL/sec, P < .05). The labrum-repaired condition (0.21 ± 0.2 mL/sec) demonstrated significantly less fluid efflux when compared with the labral-tear condition. Hip labral repair significantly prevented greater fluid efflux when compared with partial labral resection (0.60 ± 0.4 mL/sec) and reconstruction with iliotibial band autograft (0.54 ± 0.3 mL/sec; P < .05). Labral repair did not preserve fluid efflux as effectively as in the labrum-intact condition (0.21 ± 0.2 > 0.006 ± 0.008 mL/sec; P < .05). There was no difference observed in fluid efflux between the labral reconstruction, tear, or resection conditions (P > .05). Conclusion: In this human cadaveric model, hip labral repair outperforms partial labral resection and reconstruction in preserving the joint fluid seal; however labral repair does not restore fluid seal characteristics as effectively as in the labrum-intact condition. Clinical Relevance: Further prospective studies are needed to determine whether hip labral repair outperforms partial labral resection and/or reconstruction in clinical practice.

Biomechanical Performance of Rotator Cuff Repairs With Humeral Rotation A New Rotator Cuff Repair Failure Model

Background Traditional biomechanical evaluations of rotator cuff repair techniques employ cyclic loading of the supraspinatus tendon in an isolated medial direction. Purpose This study was conducted to evaluate 2 different rotator cuff repair techniques that are currently the subject of debate with cyclic loading and with internal and external humeral rotation to better simulate postoperative rehabilitation. Study Design Controlled laboratory study. Methods Nine fresh-frozen paired human cadaver shoulders (18 shoulders) were studied. A single-row repair with 2 suture anchors was compared with a double-row repair with 4 suture anchors. The shoulders were tested in a custom device to position the shoulder in neutral, 45° of internal rotation, and 45° of external rotation. Cyclic loading of the supraspinatus tendon was performed with an MTS material testing machine. Gap formation was measured and analyzed for each rotational position using the MTS device. Results For the single-row repair, average gap formation per 100 cycles in the positions of neutral, internal, and external humeral rotation was 1.47 ± 0.63, 3.11 ± 1.55, and 2.24 ± 0.94 mm, respectively. For the double-row repair, average gap formation per 100 cycles in the positions of neutral, internal, and external humeral rotation was 1.25 ± 0.54, 2.29 ± 1.10, and 1.57 ± 0.48 mm, respectively. For gapping averaged over all positions, the double-row repair had significantly less gapping than the single-row repair (P = .0109); gapping was greatest for internal rotation, followed by external rotation, and least for neutral (P < .0001). Conclusion The testing method of including a rotational component in biomechanical rotator cuff repair testing is a more realistic model of the loading conditions experienced by a repaired rotator cuff as the patient participates in postoperative rehabilitation. Double-row repair has better fixation strength than single-row repairs when exposed to cyclic loading and changes in humeral rotation position. Clinical Relevance Humeral rotation affects rotator cuff fixation and should be considered in postoperative rehabilitation.

Reverse total shoulder arthroplasty for cuff tear arthropathy: the clinical effect of deltoid lengthening and center of rotation medialization.

BACKGROUND Reverse total shoulder arthroplasty (RSA) for cuff tear arthropathy improves shoulder function and reduces pain. Implant position and soft tissue balancing are important factors to optimize outcome. Tensioning the deltoid and increasing the deltoid moment arm by medializing the center of rotation are biomechanically advantageous. The purpose of this study was to correlate RSA functional outcomes with deltoid lengthening and center of rotation medialization. MATERIALS AND METHODS This prospective cohort study enrolled 49 consecutive patients who underwent RSA for cuff tear arthropathy. Preoperative and serial postoperative physical examinations, radiographs, and American Shoulder and Elbow Surgeons and Simple Shoulder Test scores were evaluated. Deltoid lengthening and medialization of the center of rotation were measured radiographically and correlated with functional outcome scores, range of motion, and complications. RESULTS At final follow-up (average, 16 ± 10 months), 37 of 49 patients (76%) were available for analysis. Deltoid lengthening (average, 21 ± 10 mm) correlated significantly (P = .002) with superior active forward elevation (average, 144° ± 19°). Medialization of the center of rotation (average, 18 ± 8 mm) did not correlate with active forward elevation or subjective outcomes. Deltoid lengthening that achieved an acromion-greater tuberosity distance exceeding 38 mm had a 90% positive predictive value of obtaining 135° of active forward elevation. Two patients (4%) required revision surgery, and 68% of patients developed scapular notching (average grade, 1.3 ± 1.2) at final follow-up. CONCLUSION Deltoid lengthening improves active forward elevation after RSA for cuff tear arthropathy.

Investigation of the frictional response of osteoarthritic human tibiofemoral joints and the potential beneficial tribological effect of healthy synovial fluid.

OBJECTIVE This study tests the hypothesis that the natural progression of osteoarthritis (OA) in human joints leads to an increase in the friction coefficient. This hypothesis is based on the expectation that the wear observed in OA may be exacerbated by higher friction coefficients. A corollary hypothesis is that healthy synovial fluid (SF) may help mitigate the increase in the friction coefficient in diseased joints. DESIGN The friction coefficient of human tibiofemoral joints with varying degrees of OA was measured in healthy bovine SF and physiological buffered saline (PBS). Two testing configurations were adopted, one that promotes sustained cartilage interstitial fluid pressurization to investigate the effectiveness of this mechanism with advancing OA, and another that allows interstitial fluid pressure to subside to investigate the effectiveness of boundary lubrication. RESULTS Seven specimens were visually staged to be normal or mildly degenerated (stages< or =2 on a scale of 1 to 4) and nine others had progressive degeneration (stages>2 and< or =3). No statistical differences were found in the friction coefficient with increasing OA, whether in migrating or stationary contact area configurations; however, the friction coefficient was significantly lower in SF than PBS in both configurations. CONCLUSIONS The friction coefficient of human tibiofemoral cartilage does not necessarily increase with naturally increasing OA, for visual stages ranging from 1 to 3. This outcome may be explained by the fact that interstitial fluid pressurization is not necessarily defeated by advancing degeneration. This study also demonstrates that healthy SF decreases the friction coefficient of OA joints relative to PBS.