Walter R. Lowe

The 2007 Frank Stinchfield Award. The biomechanics of the hip labrum and the stability of the hip.

We explored the mechanical factors leading to the formation of labral tears and the effect of these lesions on hip kinematics at the extremes of joint motion. Using a 3D motion analysis system, the stability of six cadaveric hips was measured during loading maneuvers known to impose anterior loads on the joint margin. These measurements were repeated following venting of the capsule, and after creation of a 15-mm tear in the intact labrum. Compared to the intact hip, 43% and 60% less force was required to distract the femur by 3 mm after venting and creation of a tear. An ER torque of 177 in-lbf in 30° of flexion caused the vented and torn specimens to rotate 1.5° ± 2.7° and 7.1° ± 4.7° more than the intact specimen, and the femoral head to displace 1.21 ± 0.53 mm and 0.67 ± 0.35 mm, respectively. A breach of the integrity of labral function is shown to lead to decreased femoral stability relative to the acetabulum during extreme ranges of motion.

Cyclic Pull-Out Strength of Hamstring Tendon Graft Fixation with Soft Tissue Interference Screws Influence of Screw Length

Blunt-threaded interference screws used for fixation of hamstring tendons in anterior cruciate ligament reconstructions provide aperture fixation and may provide a biomechanically more stable graft than a graft fixed further from the articular surface. It is unknown if soft tissue fixation strength using interference screws is affected by screw length. We compared the cyclic and time-zero pull-out forces of 7 25 mm and 7 40 mm blunt-threaded metal interference screws for hamstring graft tibial fixation in eight paired human cadaveric specimens. A four-stranded autologous hamstring tendon graft was secured by a blunt-threaded interference screw into a proximal tibial tunnel with a diameter corresponding to the graft width. Eight grafts were secured with a 25-mm length screw while the other eight paired grafts were secured with a 40-mm length screw. During cyclic testing, slippage of the graft occurred as the force of pull became greater with each cycle until the graft-screw complex ultimately failed. All grafts failed at the fixation site, with the tendon being pulled past the screw. There were no measurable differences in the mean cyclic failure strength, pull-out strength, or stiffness between the two sizes of screws. Although use of the longer screw would make removal technically easier should revision surgery be necessary, it did not provide stronger fixation strength than the shorter, standard screw as had been postulated.

Effect of Lateral Meniscal Root Tear on the Stability of the Anterior Cruciate Ligament–Deficient Knee

Background: Meniscal root tears are an increasingly recognized subset of meniscal injury. The menisci are critical secondary stabilizers of the anterior cruciate ligament (ACL). The kinematic effect of lateral meniscus posterior root tear in the setting of ACL injury is not known. Purpose/Hypothesis: The purpose of this study was to determine the effect of tear of the lateral meniscal root on stability of the ACL-deficient knee. The hypothesis was that disruption of the lateral meniscal root will further destabilize the ACL-deficient knee during a simulated pivot shift. Study Design: Controlled laboratory study. Methods: Pivot-shift testing of 8 fresh-frozen cadaveric knees was performed after attachment of photoreflective flags and preparation of CT scans. Each knee was mounted in a custom activity simulator and dynamically loaded from 15° to 90° of flexion with all the permutations of the following: iliotibial band force (50, 75, 100, 125, 150, and 175 N), internal rotation moments (1, 2, and 3 N·m), and valgus moments (5 and 7 N·m). In addition, anterior stability tests were performed by applying a 90-N anterior force to the tibia at flexion angles of 15°, 30°, 45°, 60°, and 90°. During each test, the anterior tibial translation and rotation of the tibia were measured with a high-resolution multiple infrared camera motion analysis system for the following 3 conditions: ACL-intact (ACL-I), ACL-deficient (ACL-D), and ACL-deficient/lateral meniscal posterior root avulsion (ACL-D/LMR-A). Results: A pivot-shift phenomenon was observed in the ACL-D and ACL-D/LMR-A conditions. The mean tibial translation of the lateral tibial condyle during the pivot-shift maneuver was 2.62 ± 0.53 mm for the ACL-I knees, 6.01 ± 0.51 mm for the ACL-D knees (P value vs intact: .0005), and 8.13 ± 0.75 mm for the ACL-D/LMR-A knees (P value vs intact: <.0001). During the pivot-shift maneuver, translation was significantly increased in the ACL-D/LMR-A condition compared with the ACL-D condition (P = .0146). Compared with the intact group, anterior tibial translation during the Lachman maneuver also increased at 30° and 90° of flexion in the ACL-D group (P < .0001) and the ACL-D/LM group (P < .0001). No statistically significant difference was found between the ACL-D and ACL-D/LMR-A groups during the Lachman maneuver at 30° and 90° (P = .16 and .72, respectively). Conclusion: A tear of the lateral meniscal posterior root further reduces the stability of the ACL-deficient knee during rotational loading. Clinical Relevance: This study shows that lateral meniscal root injury further destabilizes the ACL-deficient knee and thus advances the concept that the lateral meniscus is a secondary stabilizer of the knee under pivot-shift loading. In the absence of stronger evidence, the study data suggest a rationale for surgical repair of lateral meniscal root tears encountered in the setting of ACL tears.

Comparison of 2 femoral tunnel locations in anatomic single-bundle anterior cruciate ligament reconstruction: A biomechanical study

PURPOSE To evaluate knee stability after anterior cruciate ligament (ACL) reconstruction using 2 modern clinically relevant single-bundle constructs. METHODS Two arthroscopic ACL reconstructions were performed on 6 fresh-frozen human cadaveric knees using bone-patellar tendon-bone autografts. The tibial tunnel was centered in the anatomic tibial footprint. The femoral tunnel was reamed through the anteromedial (AM) portal and centered alternately in either the AM portion of the femoral footprint (center-AM) or the center of the femoral footprint (center-center). Two external loading conditions were applied: (1) a 134-N anterior tibial load and (2) a 10-Nm valgus load combined with a 5-Nm internal tibial torque. Resulting kinematics were determined under 4 conditions: (1) ACL intact, (2) ACL deficient, (3) center-AM reconstruction, and (4) center-center reconstruction. RESULTS In response to anterior tibial loading, anterior translation was similar in the ACL-intact knee and the 2 reconstructions at 0° to 60° of flexion but was greater in the reconstructed specimens at 90°. In response to the complex rotatory load, internal tibial rotation (ITR) at 30° of flexion was slightly greater in center-AM knees compared with ACL-intact knees (11.0° ± 0.6° v 10.5° ± 0.6°, P = .03). At other angles tested, ITR in both reconstructions was similar to the ACL-intact knee (P > .05). When we compared the 2 reconstruction alternatives, however, center-center knees exhibited greater resistance to ITR at all angles (P < .05). CONCLUSION Anatomic single-bundle ACL reconstruction performed with the femoral tunnel placed through the AM portal restores translational and rotational knee stability to an extent that closely approximates the ACL-intact condition. When compared with the AM femoral tunnel position, a femoral tunnel positioned in the anatomic center of the femoral origin of the ACL may further improve rotatory stability without sacrificing anterior stability. CLINICAL RELEVANCE This study provides additional biomechanical evidence in support of anatomic single-bundle ACL reconstruction with tunnels positioned in the center of the femoral and tibial footprints.

Anatomic Double-Bundle Anterior Cruciate Ligament Reconstruction: Kinematics and Knee Flexion Angle–Graft Tension Relation

PURPOSE The purpose of this study was to compare the bundle tension curves and resultant knee kinematics between 2 tensioning protocols in anatomic double-bundle anterior cruciate ligament (ACL) reconstruction. METHODS Anatomic double-bundle ACL reconstruction was performed in 7 male cadaveric knees. Each graft was tensioned to 22 N under 2 conditions: (1) both bundles tensioned at 20 degrees of knee flexion (20/20 protocol) or (2) posterolateral (PL) bundle tensioned at 15 degrees and anteromedial (AM) bundle at 45 degrees (45/15 protocol). Knee kinematics were recorded in response to anterior and combined rotatory loads in the intact, ACL-deficient, and reconstructed states. Bundle tension was recorded dynamically with knee motion and during each loading test. RESULTS Tensioning both bundles at 20 degrees of knee flexion resulted in a reciprocal bundle tension pattern that was not statistically different; the PL bundle tension was greater than the AM bundle tension in full extension, and the AM bundle tension was greater than the PL bundle tension from 25 degrees to 120 degrees. In the second tensioning protocol, the AM bundle tension was significantly greater than the PL bundle tension at all flexion angles. Both tensioning protocols restored normal knee kinematics. CONCLUSIONS Bundle-tensioning protocol is a variable that has a significant effect on the bundle-loading patterns in double-bundle ACL reconstruction. The 20/20 protocol resulted in AM and PL bundle-loading patterns that were equivalent during dynamic testing, whereas the 45/15 protocol led to excessive tension in the AM bundle in full extension. We recommend equal tensioning of both bundles with the knee at 20 degrees of flexion to restore relatively normal tension curves in each bundle and to avoid excessive stress on the AM bundle. CLINICAL RELEVANCE In double-bundle ACL reconstruction, there is no consensus regarding bundle-tensioning protocols. This study provides data on the individual bundle tension curves that result from 2 commonly used tensioning protocols. These data will assist clinicians as the technique and application of double-bundle ACL reconstruction move forward.

A Biomechanical Comparison of Repair Techniques for Type II SLAP Lesions

Background Multiple options exist for repair of superior labral tears. Purpose To compare commonly used fixation techniques for superior labral tears. Study Design Biomechanical cadaveric study. Methods A comparison of the initial strengths of fixation for type II superior labral anterior posterior (SLAP) lesions was performed in three cadaveric shoulder groups, each containing seven specimens. Two groups were repaired with screw-in anchors; one group had vertical sutures, the other horizontal. Group 3 was repaired using bioabsorbable tacks. Cyclic traction was applied to the biceps tendon. Repair failure (2 mm of permanent displacement) and ultimate failure were measured. Results Specimen stiffness was similar between groups. The mean load to repair failure was 123 ± 17 N in group 1, 114 ± 11 N in group 2, and 95 ± 13 N in group 3. The mean load to ultimate failure was 163 ± 15 N, 161 ± 12 N, and 145 ± 12 N, respectively. Although the repair failure loads of groups 1 and 2 were 29% and 17%, respectively, greater than the tack group, the differences were not statistically significant (P> .05). All ultimate failures occurred at the labral-implant interface. Conclusion Initial fixation strength of tissue tack and suture anchor repairs of SLAP lesions are comparable.

The Routine Culture of Allograft Tissue in Anterior Cruciate Ligament Reconstruction

Background Allograft tissue is an acceptable alternative to autograft tissue in anterior cruciate ligament (ACL) reconstruction. However, several infections associated with tissue procurement have led some to consider routine intraoperative cultures of allograft tissue before implantation. A positive culture result presents a treatment dilemma in the asymptomatic patient. Hypothesis Treatment of culture swab—positive allograft tissue is unnecessary if there is no evidence of clinical infection. Study Design Cohort study (prognosis); Level of evidence, 2. Methods Retrospective analysis was performed on 247 cultures taken in 321 consecutive ACL reconstructions from a single surgeon. Allograft cultures were taken intraoperatively before antibiotic washing and implantation. All patients received standard prophylactic antibiotics consisting of intravenous vancomycin and perioperative cefazolin, and were routinely monitored in the postoperative period for signs of infection. Results Twenty-four of 247 (9.7%) cultures were positive after implantation. Sixteen of these (67%) grew organisms of high pathogenicity, whereas 8 (33%) were of low pathogenicity. Cultures were classified as poor, scant, or rare in all 24 patients. These patients did not receive additional antibiotics, and none went on to develop septic arthritis or wound complications. The 2 cases of septic arthritis had negative intraoperative cultures. Conclusions Treatment of low-virulence organisms or minimal growth high-virulence organisms is unnecessary if no evidence of clinical infection exists. The results may call into question the utility of routinely culturing allograft tissue as positive results did not correlate with infectious complications.

Failure Rate of Achilles Tendon Allograft in Primary Anterior Cruciate Ligament Reconstruction

PURPOSE This study was performed to determine the failure rate of patients undergoing primary anterior cruciate ligament (ACL) reconstruction with an Achilles tendon allograft by a single surgeon with the same surgical technique, graft fixation, and postoperative rehabilitation. The Achilles tendon allograft was obtained from a single source. METHODS Of 158 patients who underwent primary ACL reconstruction with Achilles tendon allograft, 144 were followed up at a mean of 40 months. The mean age was 29.5 years at the time of surgery. Evaluation included a questionnaire at serial follow-up visits, physical examination, and return to play. RESULTS Of 144 patients, 8 (5.6%) sustained traumatic reruptures or had evidence of laxity failure. Patients were divided into 4 age groups: less than 18 years, 18 to 25 years, 26 to 40 years, and 41 years or greater. Failure rates of 8.7%, 8.8%, 5.7%, and 0%, respectively, were found. A chi(2) contingency test was performed comparing patients aged 25 years or younger and those aged over 25 years with a resulting P value of .5811. No statistically significant difference between the groups of failures was seen. CONCLUSIONS The results of our study show that the failure rate for freeze-dried Achilles tendon allograft in primary ACL reconstruction was 8 of 144 (5.6%). When these patients were followed up for a minimum of 24 months, we found failure rates of 8.7%, 8.8%, 5.7%, and 0% in those aged less than 18 years, 18 to 25 years, 26 to 40 years, and 41 years or older, respectively. No statistically significant difference between the groups of failures was seen. LEVEL OF EVIDENCE Level IV, case series.

Knot Strength Varies Widely Among Expert Arthroscopists

Background: While most surgeons can tie visually appealing knots under an arthroscope, few surgeons have undergone an objective evaluation of their ability to consistently tie knots with maximum loop and knot security. Purpose/Hypotheses: The purpose of this study was to evaluate and compare variations in ultimate load to failure, 3-mm displacement (clinical failure), and knot stack height of arthroscopic suture knots tied by 73 independent expert orthopaedic arthroscopists. The hypotheses were (1) that skilled arthroscopic surgeons would be able to routinely tie arthroscopic knots of similar strength, (2) that surgeons with <10 years of clinical practice would tie stronger and more consistent knots, and (3) that surgeons who performed >200 arthroscopic shoulder cases per year would produce stronger and more consistent knots than would surgeons who performed fewer cases. Study Design: Controlled laboratory study. Methods: Each surgeon tied 5 of the same type of their preferred arthroscopic knot and half-hitch locking mechanism. Each knot was mechanically tested for ultimate load to failure and clinical failure. Results: For the 365 individual knots tested, the mean ultimate load across each knot was 231 N (range, 29-360 N). The mean clinical failure load was 139 N (range, 16-328 N). The average knot stack height among the 365 knots was 5.61 mm (range, 2.89-10.32 mm). For an individual surgeon, the standard deviations of the 5 consecutive knots tied ranged from 6 to 133 N. The ultimate load and clinical failure load for surgeons with <10 years of practice (n = 39) were 248 ± 93 N and 142 ± 56 N, respectively. The mean ± SD ultimate and clinical failure loads for surgeons with >10 years of practice (n = 34) were 211 ± 111 N and 136 ± 69 N, respectively. When knot strength was used to measure performance, significant differences existed in ultimate load (P = .001); however, there were no differences in clinical failure load (P = .329). Surgeons with <10 years of practice were able to tie knots more consistently than were surgeons in practice for >10 years, for both ultimate load (P = .018) and clinical failure load (P = .005). There was no significant difference based on number of cases performed with respect to ultimate load or clinical failure load (P = .292 and .479, respectively). There was no difference in consistency, as both groups had similar standard deviations (P = .814 for ultimate load, P = .545 for clinical failure). Conclusion: Considerable variations in knot strength exist between arthroscopic knots tied by surgeons. Study findings revealed that surgeons were unable to tie 5 consecutive knots of the same type consistently; that for both ultimate load and clinical failure load, surgeons with <10 years in practice were able to tie knots more consistently than surgeons with >10 years; and that surgeons performing >200 arthroscopic shoulder cases annually failed to tie stronger or more consistent knots than their counterparts performing fewer cases. Clinical Relevance: This variation in knot tying has the potential to affect the integrity of arthroscopic repairs. Independent objective testing of the ability to tie secure knots as part of a surgeons’ training may be necessary.

Surgical anatomy of the posterior shoulder: Effects of arm position and anterior-inferior capsular shift

The purposes of this study were to evaluate anatomically various surgical intervals to the posterior shoulder and to determine the effects of varying arm positions and anterior-inferior capsular shift (AICS) on the relation of the posterior neurovascular structures to fixed bony landmarks. Fourteen cadaveric shoulders were dissected. The posterior surgical anatomy was defined, and the distances from fixed bony landmarks to neurovascular and musculotendinous structures were determined with digital calipers. Measurements were made with the arm in various positions and repeated after AICS. The most direct anatomic approach to the posterior shoulder was through a deltoid split in the raphe from the posterolateral corner of the acromion (PLCA), followed by an infraspinatus (IS) splitting incision. The IS/teres minor interval was at the inferior aspect of the glenoid rim and was difficult to locate in all specimens. The distance to the axillary nerve from the PLCA averaged 65 mm and decreased by an average of 14 mm (22%) with abduction and by 19 mm (29%) with extension. The posterior humeral circumflex artery was located along the humeral neck and was vulnerable to injury during lateral capsular dissection. The suprascapular nerve had multiple branches to the IS with most penetrating the muscle at its inferior portion. The closest branch to the glenoid rim was an average of 20 mm medial from it. No branch entered at the level of the IS raphe. The anatomic relations of the suprascapular nerve were unchanged after AICS. On the basis of this study, surgical exposure of the posterior shoulder with a deltoid split from the PLCA, followed by an IS split, appears to be anatomically safe. The arm position should be in neutral rotation, especially if previous anterior capsular procedures have been performed, which can alter the posterior neurovascular anatomic relations.