Changes In Knee Laxity Research Articles

Bilateral changes in knee joint laxity during the first year after non-surgically treated anterior cruciate ligament injury

ObjectivesAnalyse changes in knee laxity between 3, 6, 12 and 24 months after non-surgically treated ACL injury and to analyse associations between knee laxity and knee function, self-reported knee stability, ACL-Return to Sport after Injury (ACL-RSI), fear and confidence at different timepoints during recovery. DesignProspective cohort study. Participants125 patients (67 males, mean age 25.0 ± 7.0 years) with acute ACL injury. Main outcomeLaxity was measured using KT-1000 arthrometer. Self-reported knee function was assessed using the International Knee Documentation Committee Subjective Knee Form (IKDC-SKF). Confidence and fear were assessed with questions from the ACL-RSI scale. Subjectively knee stability was assessed using SANE. ResultsKnee laxity increased bilaterally from 3 to 12 months, and in the non-involved knee from 3 to 24 months (p˂0.05), although mean change was below 1 mm. Side-to-side difference in knee laxity was correlated with IKDC-SKF (r = −0.283) and knee stability in rehabilitation/sport activities (r = −0.315) at 6 months, but not with confidence/fear. ConclusionKnee laxity increased bilaterally during the first year after non-surgically treated ACL injury, though, the mean change in knee laxity was below 1 mm and the clinical significance is unknown. Knee laxity was weakly associated with knee function and perceived knee stability. Level of evidenceLevel II Trial registrationNCT02931084

Revision Anterior Cruciate Ligament Reconstruction with the All-Soft Tissue Quadriceps Tendon Autograft Has Acceptable Early and Intermediate-Term Outcomes

The purposes were to (1) examine early to intermediate-term clinical outcomes and complications of revision anterior cruciate ligament reconstruction (ACLR) using all-soft tissue quadriceps tendon (QT) autografts, and (2) compare quadriceps strength between patients who had hamstring versus patella tendon autografts in their previous reconstruction. One hundred patients (52 males/48 females; 22.6 ± 8.0 years) undergoing revision ACLR with all-soft tissue QT autografts were prospectively followed. All revision procedures were performed by a single surgeon, using a minimally invasive graft harvest technique and suspensory fixation. Subjective assessment of knee function was obtained before and after surgery with the International Knee Documentation Committee (IKDC) survey. Postoperative knee laxity and isokinetic quadriceps strength were collected at regular intervals. Strength was reported as limb symmetry index (LSI; surgical side divided by nonsurgical side). Complications including hematomas, postoperative loss of knee extension, and graft failures were recorded. To determine clinical significance (P ≤ .05), outcomes were compared using analysis of variance or paired samples t-tests. The mean IKDC scores significantly improved (54.3 ± 13.0 vs 82.8± 13.8), with an average follow-up of 42.2 ± 21.2 months. There were no significant changes in knee laxity side-to-side differences: 6 weeks (1.2 ± 1.5 mm), 3 months (1.2 ± 1.8 mm), 6 months (1.4 ± 1.6 mm). Quadriceps LSIs significantly improved from 71.6% ± 19.3% at 6 months to 81.5% ± 19.3% at 12 months for 60°/s isokinetic testing and 76.6% ± 16.4% at 6 months to 83.9% ± 16.9% at 12 months for 180°/s testing. Graft harvest site hematomas developed in 2 patients, postoperative loss of knee extension in 4 patients, and graft failure in 11 patients. No significant differences in quadriceps or hamstrings LSIs were noted between patients with previous hamstring versus patella tendon autografts (P>.050). Revision ACLR with all-soft tissue QT autografts has acceptable early and intermediate-term outcomes with reasonable complication rates (11/80 patients with follow-up). Secondary insult to the extensor mechanism via QT autograft harvest does not adversely affect strength after prior patellar tendon versus hamstring autograft. Level IV, cases series subgroup analysis.

Second-Generation Electronic Ligament Balancing for Knee Arthroplasty: A Cadaver Study

BackgroundKnee instability is emerging as a major complication after total knee arthroplasty (TKA), with ligament laxity and component alignment listed as important contributory factors. Knee balancing remains an art and is largely dependent on the surgeon's subjective “feel.” The objectives were to measure the accuracy of an electronic balancing device to document the magnitude of correction in knee balance after soft-tissue releases and measure change in knee laxity after medial release. MethodsThe accuracy of a second-generation electronic ligament-balancing device was compared with that of 2 mechanical balancing instruments. TKA was performed in 12 cadaver knees. Soft-tissue balance was measured sequentially before TKA, after mounting a trial femoral component, after medial release, and after resecting the posterior cruciate ligament. Coronal laxity of the knee under a 10 Nm valgus moment was measured before and after medial release. ResultsThe electronic balancing instrument was more accurate than mechanical instruments in measuring distracted gap and distraction force. On average, before TKA, the flexion gap was wider than the extension gap, and the medial gap was tighter than the lateral gap. Medial release increased the medial gap in flexion and increased passive knee valgus laxity. Posterior cruciate ligament release increased the tibiofemoral gap in both flexion and extension with a greater increase in the lateral gap. ConclusionThe second-generation electronic balancing device was significantly more accurate than mechanical instruments and could record knee balance over the entire range of flexion. More accurate soft-tissue balance may enhance outcomes after TKA.

Changes in Knee Laxity and Relaxin Receptor Isoforms Expression (RXFP1/RXFP2) in the Knee throughout Estrous Cycle Phases in Rodents.

The changes in knee laxity and relaxin receptor expression at different phases of rodent estrous cycle are not known. Here, changes in the parameter were investigated in rats at different phases of the estrous cycle. Estrous cycle phases of intact female rats were determined by cytological examination of the vaginal smear. Following phase identification, blood was collected for serum hormone analyses. Knee passive range of motion (ROM) was determined by using a digital miniature goniometer. The animals were then sacrificed and patellar tendon, collateral ligaments and hamstring muscles were harvested for relaxin/insulin-like family peptide receptor 1 and 2 (RXFP1/RXFP2) analyses. Knee passive ROM was the highest at proestrus followed by diestrus and the lowest at estrus. Estrogen level was the highest at proestrus while progesterone and relaxin levels were the highest at diestrus. A strong correlation was observed between relaxin and progesterone levels. At proestrus, expression of RXFP1 and RXFP2 proteins and mRNAs were the highest at proestrus followed by diestrus and estrus. The finding shows that higher level of progesterone and relaxin in diestrus might be responsible for higher laxity of knee joint in rats.

Knee laxity after staircase exercise predicts radiographic disease progression in medial compartment knee osteoarthritis

To evaluate whether increased laxity of the knee during daily physical activities such as stair climbing is associated with progression of knee joint osteoarthritis (OA). During the years 2001-2003, 136 patients with bilateral primary medial compartment knee joint OA were enrolled in this prospective study. Baseline data collected were body mass index (BMI), muscle power, radiographic joint space width, mechanical axis on standing radiography, and anteroposterior (AP) knee laxity before and after physical exercise. After 8 years of followup, 84 patients were reexamined to assess radiographic changes. Radiographic disease progression was defined as progression of >1 grade on the Kellgren/Lawrence scale. AP knee laxity increased significantly after stair climbing. Patients with OA progression and those without progression did not differ significantly in age, sex, baseline quadriceps muscle strength, mechanical axis, joint space width, and AP knee laxity before exercise. The 2 groups of patients did, however, differ significantly in baseline BMI and change in AP knee laxity due to exercise. The risk of progression of knee OA increased 4.15-fold with each millimeter of increase in the change in AP knee laxity due to exercise and 1.24-fold with each point increase in the BMI. Our results indicate that patients with OA progression have significantly greater changes in knee joint laxity during physical activities and a higher BMI than patients without OA progression. These findings suggest that larger changes in knee laxity during repetitive physical activities and a higher BMI play significant roles in the progression of knee OA.

Why Do Girls Sustain More Anterior Cruciate Ligament Injuries Than Boys?

Sport is the leading cause of injury among adolescents and girls incur more non-contact anterior cruciate ligament (ACL) ruptures than boys, with this gender disparity in injury incidence apparent from the onset of puberty. Although the mechanisms for this gender disparity in ACL injuries are relatively unknown, hormonal, anatomical and biomechanical factors have been implicated. Puberty is associated with rapid skeletal growth and hormonal influx, both of which are thought to contribute to alterations in ACL metabolic and mechanical properties, as well as changes in lower limb strength and flexibility, ultimately influencing landing technique. Therefore, the aim of this review is to explain (i) the effects of changes in estrogen levels on the metabolic and mechanical properties of the ACL; (ii) changes in musculoskeletal structure and function that occur during puberty, including changes in knee laxity, and lower limb flexibility and strength; and (iii) how these hormonal and musculoskeletal changes impact upon the landing technique displayed by pubescent girls. Despite evidence confirming estrogen receptors on the ACL, there are still conflicting results as to how estrogen affects the mechanical properties of the ACL, particularly during puberty. However, during this time of rapid growth and hormonal influx, unlike their male counterparts, girls do not display an accelerated muscle strength spurt and the development of their hamstring muscle strength appears to lag behind that of their quadriceps. Throughout puberty, girls also display an increase in knee valgus when landing, which is not evident in boys. Therefore, it is plausible that this lack of a defined strength spurt, particularly of the hamstring muscles, combined with the hormonal effects of estrogen in girls, may contribute to a more ‘risky’ lower limb alignment during landing, in turn, contributing to a greater risk of ACL injury. There is, however, a paucity of longitudinal studies specifically examining the lower limb musculoskeletal structural and functional changes experienced by girls throughout puberty, as well as how these changes are related to estrogen fluctuations characteristic of puberty and their effects on landing biomechanics. Therefore, further research is recommended to provide greater insight as to why pubescent girls are at an increased risk of non-contact ACL injuries during sport compared with boys. Such information will allow the development of evidence-based training programmes aimed at teaching girls to land more safely and with greater control of their lower limbs in an attempt to reduce the incidence of ACL ruptures during puberty.

Paper 89: Initial ACL Graft Tension and Changes in Knee Laxity During Healing

Paper 89: Initial ACL Graft Tension and Changes in Knee Laxity During Healing

Effects of cyclic loading on the tensile properties of human patellar tendon

Bone–patellar tendon-bone (BPTB) graft is a popular choice for ACL reconstruction. These grafts are subjected to cyclic loading during the activities of daily living. Significant knee laxity is observed in reconstructed knee shortly after reconstruction. The source of this laxity is not clear. The change in the tensile properties of the graft due to cyclic loading can be one of the reasons for the change in knee laxity. Twenty patellar tendons from fresh frozen cadaver knees were cyclically loaded at a stress amplitude equivalent to 33% of the failure strength of the contralateral patellar tendon for 5000 cycles at 1.4 Hz. They were then tested in tension to failure. Failure properties and the low load properties such as toe-region modulus were calculated. The results were compared with those of contralateral patellar tendons that were not subjected to cyclic loading before testing to failure. Fatigue loading did not alter the failure and low load properties with the exception of failure strain which decreased by about 10% (P < .05). Cyclically loaded patellar tendons with higher tissue mass density possess higher strength, modulus of elasticity, toughness, and transition stress (P < .05). The results indicate that there is no significant change in graft properties because of cyclic loading with the above load magnitude. The change in knee laxity observed after reconstruction, hence, is not because of change in graft properties due to moderate cyclic loading. Other factors, such as plastic deformation (yielding) of the graft, might play a role in increased knee laxity after reconstruction.

Biomechanical Function of Anterior Cruciate Ligament Remnants: How Long Do They Contribute to Knee Stability After Injury in Patients With Complete Tears?

This study aimed to evaluate the biomechanical function of anterior cruciate ligament (ACL) remnants in anteroposterior and rotational knee stability in patients with a complete ACL injury. ACL remnants were classified into 5 morphologic patterns: group 1, bridging between the posterior cruciate ligament and tibia; group 2, bridging between the intercondylar notch and tibia; group 3, partial rupture of the posterolateral bundle; group 4, partial rupture of the anteromedial bundle; and group 5, no substantial ACL remnants. The decision of whether the remaining bundle represented partial or complete rupture of the ACL was made based on physical, magnetic resonance imaging, and arthroscopic findings in a comprehensive manner. Patients in groups 1 (n = 18) and 2 (n = 12) underwent intraoperative arthrometry with a navigation system before and immediately after resection of the ACL remnant. The effects of chronicity (duration between injury and surgery) and ACL remnant pattern on changes in knee laxity after debridement of the ACL remnant were investigated. Chronicity had a significant effect on changes in anteroposterior knee laxity evaluated at 30° of knee flexion after resection of the ACL remnant (change in laxity of 2.22 mm for chronicity ≤1 year and 0.17 mm for chronicity >1 year). Chronicity did not influence changes in rotational knee stability after resection of the remnant. There were no significant differences between groups 1 and 2 with regard to any of the evaluated changes in knee stability. In groups 1 and 2 ACL remnants contributed to anteroposterior knee stability evaluated at 30° of knee flexion for up to 1 year after injury, beyond which this biomechanical function was lost. Chronicity and remnant pattern did not influence changes in rotational knee stability after resection of the remnant. Level III, diagnostic study of nonconsecutive patients.

Knee laxity measurements after anterior cruciate ligament reconstruction, using either bone–patellar–tendon–bone or hamstring tendon autografts, with special emphasis on comparison over time

The aims of the study were to analyse the change in knee laxity over time after anterior cruciate ligament (ACL) reconstruction, using either bone-patellar-tendon-bone (BPTB) or hamstring (HS) tendon autografts, and to compare the knee laxity measurements between the study groups both pre-operatively and on multiple follow-up occasions. Another aim was to compare the radiographic findings in terms of degenerative changes between the study groups. A randomised series of 71 patients, who underwent ACL reconstruction using BPTB or HS tendon autografts and interference screw fixation, were included in the study. Of these patients, 47/71 (66%) attended a clinical examination, including laxity measurements using the KT-1000 arthrometer, pre-operatively and on four post-operative occasions; 6 months, 1 year, 2 years and 7 years after the reconstruction. The BPTB group consisted of 22 patients, while there were 25 patients in the HS group. There were no significant differences in the mean side-to-side knee laxity between the BPTB and the HS group pre-operatively or at the follow-up examinations. There was a tendency towards a reduction in side-to-side knee laxity over time in both groups, measured with the KT-1000 arthrometer. The decrease was significant when analysing the injured and uninjured knee separately (injured side p < 0.001 (BPTB) and p = 0.005 (HS), uninjured side p = 0.008 and p = 0.042, respectively). Forty-four patients (BPTB 21, ST 23) underwent a radiographic assessment at the 7-year follow-up, which revealed no significant differences between the study groups in terms of osteoarthritic findings classified according to the Fairbank and Ahlbäck rating systems. In overall terms, osteoarthritis was identified in 16% (BPTB 19%; ST 13%; n.s.) according to the Ahlbäck rating system and 68% (BPTB 67%; ST 70%; n.s.) according to the Fairbank rating system. There were no significant differences in knee laxity measurements between the two study groups pre-operatively or at 7 years. A decrease in knee laxity over time was seen in both groups. There were no significant differences between the BPTB and ST groups in terms of osteoarthritic findings at 7 years.

Changing Hormone Levels during the Menstrual Cycle Affect Knee Laxity and Stiffness in Healthy Female Subjects

Background Whether knee laxity varies throughout the menstrual cycle remains controversial. As increased laxity may be a risk factor for anterior cruciate ligament (ACL) injury, further research is warranted. Hypothesis Variation in estradiol and progesterone levels during the menstrual cycle influences knee laxity and stiffness. Study Design Case control study; Level of evidence, 3. Methods The serum estradiol and progesterone levels of 26 healthy female subjects were recorded in the follicular phase, ovulation, and the luteal phase. Knee joint laxity was assessed using a standard knee arthrometer at the same intervals. Stiffness changes in the load-displacement curve were determined. Hormone levels across the cycle were compared between responders and nonresponders, defined by whether changes in knee laxity at 89 N occurred. Results Greater laxity at 89 N during ovulation was observed (ovulation: 5.13 ± 1.70 mm vs luteal: 4.55 ± 1.54 mm, P =. 012). In knee laxity testing at manual maximum load, greater laxity was noticed during ovulation (14.43 ± 2.60 mm, P =. 018), as compared with the follicular phase (13.35 ± 2.53 mm). A reduction in knee stiffness of approximately 17% (ovulation: 12.48 ± 5.46 N/mm vs luteal: 15.02 ± 7.71 N/mm, P =. 042) during ovulation was observed. However, there were no differences in hormone levels between responders and nonresponders at 89 N. Conclusion Female hormone levels are related to increased knee joint laxity and decreased stiffness at ovulation. To understand subject variations in knee joint laxity during the menstrual cycle in female athletes, further investigation is warranted.

Relationship between knee joint laxity and knee joint mechanics during the menstrual cycle

Background:An increase in knee laxity during the menstrual cycle may increase the risk of anterior cruciate ligament injury.Objective:To investigate whether changing knee laxity during the menstrual cycle correlates with changing...

Differences in Lower Extremity Anatomical and Postural Characteristics in Males and Females Between Maturation Groups

Descriptive, cross-sectional. We compared lower extremity anatomical characteristics in males and females between different maturation groups. Sex differences have been observed in lower extremity anatomical characteristics. While the reasons contributing to these sex differences in adults are unknown, there is evidence that anatomy and posture change considerably during growth and development. One hundred seventy-three young athletes (age range, 9-18 years) were assessed for stage of maturation and placed into 1 of 3 groups, according to Tanners stages 1 and 2 (MatGrp1), 3 and 4 (MatGrp2), and 5 (MatGrp3). Participants were measured for pelvic angle, hip anteversion, quadriceps angle, tibiofemoral angle, femur length, tibial length, genu recurvatum, tibial torsion, navicular drop, general joint laxity, and anterior knee laxity. Data were compared by sex and maturation group. When comparing maturation groups, limb length, pelvic angle, and tibial torsion increased with maturation, and anterior knee laxity, genu recurvatum, tibiofemoral angle, and foot pronation decreased with maturation. Females had greater general joint laxity, hip anteversion, and tibiofemoral angles, and shorter femur and tibial lengths than males, regardless of maturation group. Maturational changes in knee laxity and quadriceps angles were sex dependent. We observed a general change of posture with maturation that began with greater knee valgus, knee recurvatum, and foot pronation in MatGrp1, then moved toward a relative straightening and external rotation of the knee, and supination of the foot in later maturation groups. While the majority of the measures changed similarly in males and females across maturation groups, decreases in quadriceps angles and anterior knee laxity were greater in males compared to females, and females were observed to have a more inwardly rotated hip and valgus knee posture, compared to males, particularly in later maturation groups.

The Effects of Running Durations on Anterior Knee Laxity in Healthy Recreational Athletes

Several studies reported increases in anterior knee laxity after running or exercises. The magnitude of changes in laxity after exercise was suggested to be fixed regardless of the amount of the exercise load. To date, the amount of changes in knee laxity after running or exercises load changes has not been extensively examined. PURPOSE: To examine the effect of change in the training load (mainly running duration) on anterior knee laxity in healthy recreational athletes. METHODS: Nine healthy recreational athletes (age = 25.3 ± 5.5 years, weight = 78.7 ± 10.4 kg, and height = 176.1 ± 7.8 cm) ran at self selected speed for 14, 19, 24, and 34 minutes. Knee Arthrometer was used to measure the anterior tibial displacement at 30 Ib. before and after running. 2X2 ANOVA was used with global ? set at 0.05. RESULTS: Two-way ANOVA showed 1) no significant interaction between running durations and testing sessions (p = 0.1), 2) no significant main effect of running durations (p = 0.65), but 3) significant main effect of testing sessions (p = 0.006) indicating increased anterior knee laxity after running. CONCLUSIONS: Running induces anterior knee laxity regardless of the running duration.

The Role of the Medial Collateral Ligament and Posteromedial Capsule in Controlling Knee Laxity

Background The medial aspect of the knee has a complex capsular structure; the biomechanical roles of specific structures are not well understood. Hypothesis The 3 strong stabilizing structures, the superficial and deep medial collateral ligaments and the posteromedial capsule, make distinct contributions to controlling tibiofemoral laxity. Study Design Controlled laboratory study. Methods Changes in knee laxity under anterior-posterior drawer, valgus, and internal-external rotation loads were found by sequential cutting in 18 cadaveric knees. Three cutting sequences allowed the roles of the 3 structures to be seen in isolation and in combination. Some force contributions were also calculated. Results The posteromedial capsule controlled valgus, internal rotation, and posterior drawer in extension, resisting 42% of a 150-N drawer force when the tibia was in internal rotation. The superficial collateral ligament controlled valgus at all angles and was dominant from 30° to 90° of flexion, plus internal rotation in flexion. The deep collateral ligament controlled tibial anterior drawer of the flexed and externally rotated knee and was a secondary restraint to valgus. Conclusion Distinct roles in controlling tibiofemoral laxity have been found for these structures that vary according to knee flexion and tibial rotation. Clinical Relevance The restraining functions demonstrated provide new information about knee stabilization, which may allow better evaluation of structural damage at the medial aspect of the knee.

Changes in Knee Laxity and Ligament Force After Sectioning the Posteromedial Bundle of the Posterior Cruciate Ligament

Our purpose was to evaluate the role of the posteromedial (PM) bundle of the native posterior cruciate ligament (PCL) in restraining posterior tibial translation and the effects of sectioning of the PM bundle on PCL forces. The PCL's femoral origin was mechanically isolated by use of a cylindrical coring cutter, and a cap of bone containing the ligament fibers was attached to a load cell that recorded resultant force in the ligament as the knee was passively extended from 120 degrees to 0 degrees without and with simulated tibial loading conditions. Anteroposterior laxity was also measured after load cell installation. The PM bundle was cut at its femoral origin, and all tests were repeated. Cutting the PM bundle produced small but statistically significant increases in mean laxity at 0 degrees (+1.06 mm) and 10 degrees (+0.83 mm) of flexion; mean laxities at 30 degrees, 45 degrees, 70 degrees, and 90 degrees were unchanged. Forces in the remaining anterolateral bundle were not significantly different from those in the intact ligament for any mode of tibial loading, with the exception of the valgus moment, where sectioning of the PM bundle significantly reduced the PCL force at 0 degrees and 5 degrees of flexion. The relatively small increases in mean laxity after cutting of the PM bundle show that it plays a minor role in restraining posterior tibial translation. The minor changes in ligament force profiles after cutting of the PM bundle indicate that the remaining anterolateral bundle fibers continued to be loaded in a near-normal fashion. This study helps to elucidate the function of the PM bundle in the native PCL. Because only small changes were seen in the biomechanical parameters tested, the rationale for reconstructing this bundle of the PCL could be questioned.

Variation in anterior cruciate ligament scar pattern: Does the scar pattern affect anterior laxity in anterior cruciate ligament-deficient knees?

This prospective study documented patterns of scar formation after anterior cruciate ligament (ACL) rupture in order to test the hypothesis that ACL remnants can contribute to anterior knee passive motion limits tested with a ligament arthrometer. Prospective cohort study. Forty-eight consecutive patients undergoing ACL reconstructions had intra-operative ligament arthrometry testing before and immediately after preparation of the notch and debridement of the ACL remnant. Patterns of scar formation were compared with changes in knee laxity after debridement of the ACL remnant. Eighteen patients (38%) had ligament scarring to the posterior cruciate ligament (group 1). Four patients (8%) had scar tissue that appeared to extend from the ACL fibers to the roof of the notch (group 2). Six ACL remnants (12%) appeared to have healed to the lateral wall of the notch or the medial aspect of the lateral femoral condyle in a position anterior and distal to the ACL anatomic footprint (group 3). In 20 patients (42%), there was no identifiable ligament tissue remaining (group 4). Changes in anterior laxity were associated with the specific pattern of scar formation within the notch. The greatest increase in anterior laxity after debridement was observed in knees in which the injured ACL had an aberrant reattachment to the femur: group 1 (mean, -1.3 mm; P < .01), group 2 (mean, -3.4 mm; P < .05), and group 3 (mean, -4.3 mm; P < .05). In group 4, the change in knee laxity was not significant (mean, 0.2 mm; 95% CI, -0.29 to 0.74 mm). Overall, 14 of 48 knees (29%) loosened more than 2 mm after ACL resection ( P < .01). Resection of the ACL scar resulted in a measurable increase in passive anterior laxity in a subset of ACL-deficient knees. This increase in anterior laxity occurred in patients whose ligament healed to the femur, effectively crossing the joint. When performing arthroscopy without reconstruction in ACL-injured knees, we recommend caution in resecting the torn ACL or scar tissue because removal of this tissue contributed to increased anterior laxity in some ACL-deficient knees. Level II, diagnostic study of consecutive patients.

Relationship between sex hormones and anterior knee laxity across the menstrual cycle.

To comprehensively quantify through daily, serial measures changes in knee laxity as a function of changing sex-hormone levels across one complete menstrual cycle. Twenty-five females, 18 - 30 yr, body mass index < or = 30, who reported normal menstrual cycles (28-32 d) over the past 6 months participated. Participants were tested daily across one complete menstrual cycle; 5-7 cc of venous blood were withdrawn to assay serum levels of estradiol, progesterone, and testosterone. Knee laxity was measured as the amount of anterior tibial displacement at 133 N, using a standard knee arthrometer. To evaluate the relationship of knee laxity to changes in sex hormone concentrations, a multiple linear regression model with the possibility of a time delay was performed on each individual subject and the group as a whole. Individual regression equations revealed an average of 63% of the variance in knee laxity was explained by the three hormones and their interactions. All three hormones significantly contributed to the prediction equation, and the amount of variance explained was substantially greater when a time delay was considered. On average, knee laxity changed approximately 3, 4, and 4.5 d after changes in estradiol, progesterone, and testosterone, respectively. When females were analyzed as a group, only 8% of the variance in knee laxity was explained by sex-hormones levels. Changes in sex hormones mediate changes in knee laxity across the menstrual cycle. However, the strength of this relationship, the relative contribution of each hormone, and the associated time delay are highly variable between women. This individual variability is consistent with the variability in menstrual cycle characteristics among women.

Sex Hormones Explain More Variance In Anterior Knee Laxity Across The Menstrual Cycle When A Time Delay Is Considered

0258 PURPOSE: To determine the relationship between daily changes in anterior knee joint laxity and sex-hormone levels across one complete menstrual cycle, with and without a time delay considered. METHODS: 22 females (23.0±3.5 yrs, 163.4±5.6cm, 65.0±11.6 kg, 24.3±3.5 BMI) who reported normal menstrual cycles (28–32 days) were tested daily across one complete cycle. Serum levels of estradiol (pg/mL), progesterone (ng/mL), and testosterone (ng/mL) were assayed. Knee laxity was measured with a standard knee arthrometer, and the displacement (mm) obtained at 133N was used for statistical analysis. A multiple linear regression model with the possibility of a time delay (range 0–8 days) was performed on individual subjects, and the group as a whole. RESULTS: Individual regression equations revealed that, on average, 63.3±7.7% of the variance in knee laxity was explained by the three sex hormones and their interactions when a time delay was considered. The strongest relationship was noted when knee laxity changed approximately 3.1±2.3, 3.9±2.9 and 4.5±2.4 days following changes in estradiol, progesterone and testosterone respectively. This model explained substantially more variance in knee laxity than when no time delay was allowed (25.9+15.8%), and when only estradiol (18.6+10.1%) or estradiol + progesterone and their interaction (36.7+12.5%) were entered in the model with a time delay. When females were analyzed as a group, sex-hormone levels explained only 8% of the variance in knee laxity. CONCLUSIONS: Estradiol, progesterone and testosterone each contributed to changes in knee laxity across the cycle, with this relationship strengthened at some time delay. However, consistent with the variability in menstrual cycle characteristics between females, the strength of this relationship, the relative contribution of each hormone, and the associated time delay were also variable between females. Supported by NIH Grants RO3 AR47178 and MO1 RR00847, and through a cooperative agreement [U54 HD28934] as part of the Specialize Cooperative Centers Program in Reproductive Research.

Biomechanical effects of medial–lateral tibial tunnel placement in posterior cruciate ligament reconstruction

With most posterior cruciate (PCL) reconstruction techniques, the distal end of the graft is fixed within a tibial bone tunnel. Although a surgical goal is to locate this tunnel at the center of the PCL’s tibial footprint, errors in medial–lateral tunnel placement of the tibial drill guide are possible because the position of the tip of the guide relative to the PCL’s tibial footprint can be difficult to visualize from the standard arthroscopy portals. This study was designed to measure changes in knee laxity and graft forces resulting from mal-position of the tibial tunnel medial and lateral to the center of the PCL’s tibial insertion. Bone–patellar tendon–bone allografts were inserted into three separate tibial tunnels drilled into each of 10 fresh-frozen knee specimens. Drilling the tibial tunnel 5 mm medial or lateral to the center of the PCL’s tibial footprint had no significant effect on knee laxities; the graft pretension necessary to restore normal laxity at 90° of knee flexion (laxity match pretension) with the medial tunnel was 13.8 N (29%) greater than with the central tunnel. During passive knee flexion–extension, graft forces with the medial tibial tunnel were significantly higher than those with the central tunnel for flexion angles greater than 65° while graft forces with the central tibial tunnel were not significantly different than those with the lateral tibial tunnel. Graft forces with medial and lateral tunnels were not significantly different from those with a central tunnel for 100 N applied posterior tibial force, 5 N m applied varus and valgus moment, and 5 N m applied internal and external tibial torque. With the exception of slightly higher graft forces recorded with the medial tunnel beyond 65° of passive knee flexion, errors in medial–lateral placement of the tibial tunnel would not appear to have important effects on the biomechanical characteristics of the reconstructed knee.