Normal Knee Alignment Research Articles

Impact of asymptomatic genu recurvatum on patellar mobility in young males

BACKGROUND: Genu recurvatum is one of the most commonly presented lower extremity postural malalignments in individuals. Though genu recurvatum and its impact on impaired knee proprioception, anterior cruciate injuries and posterior soft tissue dysfunctions are reported, its association with patellar mobility is scarcely reported and warrants exploration. OBJECTIVES: To evaluate the medial and lateral patellar mobility differences in adult young males with genu recurvatum and normal knee alignment. METHODS: The ethical approval for this cross-sectional study protocol was obtained and the study was conducted in Research Department of Alva’s College of Physiotherapy and Research Centre, Moodubidire, DK, Karnataka, India. The study participants were recruited through an institutional-based musculoskeletal and sports clinic. The estimated sample size for this study was 174. A total of 87 young males with genu recurvatum and 87 young males with normal knee alignment fulfilling the selection criteria were enrolled in two groups. Participants' knee joint was examined by an assessor and individuals with > 5⁰ knee hyperextension were assigned to genu recurvatum group, and individuals with knee extension < 5⁰ from neutral were assigned to the normal knee alignment group. Further, the patellar glide test was performed to examine the presence of patellar hypermobility in both groups. RESULTS: The mean age of the participants in genu recurvatum and normal knee alignment group was 22.04 + 1.860 and 21.91 + 1.869, respectively. A significant higher proportion (86.2%) of participants with genu recurvatum identified with patellar hypermobility compared to normal knee alignment. Within the genu recurvatum subjects, 66.66& and 19.54% were observed to have medial and lateral patellar hypermobility. The odds for occurrence of patellar hypermobility in genu recurvatum was estimated to be 13.007 (95%, CI, 5.481 – 30.866), respectively. CONCLUSION: The study result suggests that medial patellar hypermobility is more common in individuals with genu recurvatum. Further study investigating on the mechanism contributing towards medial patellar mobility in genu recurvatum populations could validate the present study findings.

Kinematic study of the overall unloading brace for the knee

ObjectiveTraditional knee braces unloading forces primarily from a single compartment are insufficient for patients with knee injuries or knee osteoarthritis (KOA) involving multiple compartments. We investigated how knee kinematics were altered by an overall unloading brace (OUB) designed to unload both the medial and lateral tibiofemoral (TF) compartments simultaneously during dynamic movement. MethodsGait analysis was performed on 32 adults with normal knee alignment and no history of knee disease. Three-dimensional (3D) knee kinematic data collected during treadmill walking (3 km/h) and jogging (5 km/h) with an optical motion capture system were compared with versus without the OUB. ResultsIn the stance phase, wearing the OUB, versus not wearing it, increased the proximal-distal translational range of motion (ROM) of the knee by 4.04 mm (Effect size, ES = 0.97) during walking and by 3.43 mm (ES = 0.97) during jogging, decreased abduction-adduction rotational ROM by 3.09°(ES = 1.05) during walking and by 2.88°(ES = 1.50) during jogging, and decreased internal-external rotation by 2.14°(ES = 0.81) during walking and by 4.66°(ES = 1.61) during jogging. In the swing phase, the OUB increased proximal-distal translational ROM by 12.64 mm (ES = 1.31) during walking and by 9.23 mm (ES = 0.92) during jogging, decreased abduction-adduction rotational ROM by 2.83°(ES = 0.54) during walking and by 3.37°(ES = 0.67) during jogging, and decreased internal-external rotational ROM by 2.71°(ES = 0.68) during jogging. ConclusionsOUB use increased proximal-distal translation while reducing abduction-adduction rotation. This effect may increase the joint gap of the tibiofemoral joint, thereby reducing joint stress, and may contribute to disease rehabilitation in the knee of clinical orthopedics, rehabilitation, and sports medicine fields. However, additional studies are needed to assess the range of possible clinical and prophylactic benefits of OUB.

Lateral shift of the femoral condyle after total knee arthroplasty: simulation using 2D-templates of the medial pivot design on knee radiographs of young Japanese patients

BackgroundTotal knee arthroplasty (TKA) is an established surgical treatment for advanced knee osteoarthritis by which patients can expect improvement of knee pain and function. Although many surgeons have investigated limb alignment after TKA, changes in coronal positional relation between the femur and tibia are not known well.MethodsRadiographs of 105 knees of young Japanese patients between 20 and 49 years-old (60 men and 45 women) without osteoarthritic changes who received arthroscopic surgeries at our hospital were used in this study. Using 2D-templates of the medial pivot design (the FINE total knee), we simulated TKA on a SYNAPSE-PACS software. First, the femoral component was placed in normal knee alignment and then was merged to the medial concave of the insert where the tibial component was placed in neutral alignment. The length of the mediolateral shift of the femoral component was measured as an estimate of lateral shift of the femoral condyle, of which association with radiographic parameters including the femorotibial angle (FTA), lateral distal femoral angle (LDFA), and medial proximal tibial angle (MPTA) was analyzed. Subjects were classified into three groups according to the femoral component size that was chosen in simulation of TKA, and the lateral shift of the femoral condyle was compared between groups.ResultsThe estimated mean lateral shift of the femoral condyle was 5.99 ± 1.98 mm and was greater in males than females (p < 0.05). Also, it was most highly correlated with the medial proximal tibial angle (MPTA) (r = − 0.553, p < 0.01). A group receiving larger component sizes significantly shifted more laterally compared with a group receiving smaller component sizes (p < 0.01).ConclusionsThese results suggest that the coronal positional relation between the femur and tibia is altered and subsequent ligament imbalance may occur after mechanically aligned TKA using the medial pivot design.

Poster 239: Limb Malalignment Fails to Influence Clinical Outcomes of Meniscal Repair

Objectives:Lower limb malalignment causes differences in tibiofemoral contact pressures and may influence outcomes following meniscal repair. Our objective was to evaluate clinical outcomes of meniscal repair in malaligned knees to determine if limb malalignment portends an inferior outcome. We hypothesized that medial meniscus repairs performed in varus knees and lateral meniscus repairs performed in valgus knees would result in poorer patient-reported outcomes when compared to a neutrally aligned knee.Methods:Patients who underwent meniscal repair at a single institution between 2006 and 2018 were identified by retrospective chart review. Patients between the ages of 18 and 65 with full-length weight bearing lower limb radiographs were included. Patients with varus alignment (> 3 degrees) and a medial meniscus repair, or valgus alignment (>3 degrees) and a lateral meniscus repair were considered “at-risk”. Outcomes were assessed through identification of additional surgery on the index meniscus and patient-reported outcome measures (PROMs): Knee Injury and Osteoarthritis Outcome Score (KOOS), Marx activity score, and International Knee Documentation Committee subjective score (IKDC). Failure rates and PROMs were compared between the at-risk and not at risk groups.Results:A total of 58 patients were included with a mean follow-up of 1.6 years. A total of 12 patients were classified as “at-risk”. Repeat surgery on the index meniscus was performed in 1 of 12 “at risk” patients (8.3%) and 7 of 46 (15.2%) in the “not at risk” group (p = 1.00). There were no significant differences between the two groups in KOOS subscales: pain (82.8 vs 85.6, p = 0.55), symptoms (78.2 vs 80.8, p = 0.64), ADLs (88.4 vs 92.9, p = 0.27), Sport/Rec Function (63.8 vs 69.2, p = 0.57), or QOL (58.9 vs 62.3, p = 0.69). There was also no difference in IKDC score (66.9 vs 72.5, p = 0.41) or Marx score (4.2 vs 5.0, p = 0.63) between the two groups.Conclusions:Pre-operative knee malalignment does not appear to negatively influence clinical outcomes of meniscal repair when compared to normal knee alignment.Table 1.Patient-Reported Outcome Scores

Post operative correlation of femoral tibial components with knee alignment using roentgenographic index in patients undergoing total knee arthroplasty in a tertiary referral centre

Total knee arthroplasty is the leading surgical treatment for advanced osteoarthritis of the knee. Despite its efficiency, approximately twenty percent of the cases are dissatisfied with the outcome. Mal positioning of components results in loosening, which has long-term consequences. As a result, proper sizing and placement are important for optimal functional and long-term outcomes. Achieving limb alignment, good soft tissue balance and pain relief are the primary goals of the surgeon upon completion of total knee replacement (TKA). The aim of this study was to determine the accuracy of placement of femoral and tibial components post-operatively in relation to knee alignment using a roentgenographic index. This is a prospective study conducted in a tertiary care referral hospital, we included a total of fifty cases who underwent total knee arthroplasty from the year 2019 to 2020. Post-operative radiographic parameters were measured using digital software and compared using roentgenographic indexes as described by Lotke et al. Out of the fifty Total Knee Arthroplasty cases, twenty-eight knees had perfectly positioned tibial and femoral prosthesis, fifteen cases had good position of both the components. Tibial component alignment angle (β = 90°) in relation to mechanical axis in coronal plane was seventy six percent; fourteen percent of the cases were in native knee varus. Femoral component alignment angle (α) with acceptable anatomical valgus (0-7°) were more than eighty percent of the cases. 85.5 was the mean roentgenographic index which was strongly correlatable with other similar studies. With good clinical acumen and using conventional alignment system, near to normal knee alignment in total knee arthroplasty is achievable.

Sex Differences in Iliotibial Band Strain under Different Knee Alignments.

Increased strain of the iliotibial band (ITB) is a plausible contributing factor for the development of iliotibial band syndrome (ITBS). Although several studies have found relationships between the strain of the ITB and kinematic factors during running, the associations of the ITB strain with knee alignment and sex, which are considered intrinsic factors, are not well understood. To clarify the sex differences in the ITB strain between genu varum and normal knee alignments in different postures. Observational cross-sectional study. Laboratory research within a university. Forty-four healthy recreational athletes (21 men and 23 women) volunteered for this study and were divided into four groups by sex and knee alignment: men with genu varum alignment, men with normal knee alignment, women with genu varum alignment, and women with normal knee alignment. An ultrasound real-time elastography (RTE) unit was used for distal ITB strain measurements in weight bearing and for different non-weight-bearing: neutral, knee flexion, hip adduction, and hip adduction with knee flexion. Gender information and the intercondylar distance data were collected to divide the participants into two groups. Main Outcome was the ITB strain (strain ratio) measured by the RTE. There were no significant differences in neutral and hip adduction postures among the four groups. However, during weight-bearing, the women's genu varum group (6.91 ± 1.69; Mean ± SD) exhibited greater strain than both the men's normal group (3.50 ± 1.04, P = .005) and the women's normal group (4.42 ± 1.42, P = .048). In addition, there were significant positive correlations between the intercondylar distance and the ITB strain during weight-bearing (r = 0.315, P = .037). The women's genu varum group exhibited a higher ITB strain during weight-bearing, which may be related to the high incidence of ITBS in women athletes. Furthermore, the changes in alignment and muscle activities during weight-bearing could influence the strain of the ITB. III.

Imaging of knee implants and related complications.

Various types of knee arthroplasty implants are available depending on the number of knee compartments to be replaced and ligament stability. Unlike unicompartmental arthroplasty, the aim of total knee replacement is to maintain normal knee alignment. EOS X-ray imaging in the coronal and sagittal planes is the best modality for measuring the reference axes of the knee, but may by complemented by CT scans in the transverse plane. In addition to implant-related complications such as loosening and polyethylene wear, complications of the knee extensor mechanism are sometimes observed. Conventional radiography remains the first-line diagnostic modality in the event of post-knee replacement pain or instability. Ultrasound and CT imaging may also be helpful to make diagnosis.

Relationship between paraspinal muscles fat infiltration and daily activity function in patients with lumbar spinal stenosis

sagittal (r= .937) and transverse planes (r= .883); it also showed good correlationwith the hipmotion in the transverse planes (r= .883). On the contrary, Individuals with genu valgum walked with the frontal knee motion poorly correlated with the knee motion in the sagittal, transverse planes, or hip motion in the transverse planes (r< .15). The results indicated individualswith genuvalgumwalked with more knee valgus and internal rotation during the early stance to respond to load, a kinematic pattern thatmight repetitively over-stretch the anterior cruciate ligament and result in knee instability. Conclusion(s): Correlational patterns of the knee and hip kinematics during the early stance phase were significantly different in adults with genu valgum and normal knee alignment. Implications: Poor coupling between movements of the sagittal, frontal, and transverse planes with increased valgus and internal rotation of the tibiofemoral joint during the early stance may be associated with knee instability.

Assessing the local mechanical environment in medial opening wedge high tibial osteotomy using finite element analysis.

High-tibial osteotomy (HTO) is a surgical technique aimed at shifting load away from one tibiofemoral compartment, in order the reduce pain and progression of osteoarthritis (OA). Various implants have been designed to stabilize the osteotomy and previous studies have been focused on determining primary stability (a global measure) that these designs provide. It has been shown that the local mechanical environment, characterized by bone strains and segment micromotion, is important in understanding healing and these data are not currently available. Finite element (FE) modeling was utilized to assess the local mechanical environment provided by three different fixation plate designs: short plate with spacer, long plate with spacer and long plate without spacer. Image-based FE models of the knee were constructed from healthy individuals (N = 5) with normal knee alignment. An HTO gap was virtually added without changing the knee alignment and HTO implants were inserted. Subsequently, the local mechanical environment, defined by bone compressive strain and wedge micromotion, was assessed. Furthermore, implant stresses were calculated. Values were computed under vertical compression in zero-degree knee extension with loads set at 1 and 2 times the subject-specific body weight (1 BW, 2 BW). All studied HTO implant designs provide an environment for successful healing at 1 BW and 2 BW loading. Implant von Mises stresses (99th percentile) were below 60 MPa in all experiments, below the material yield strength and significantly lower in long spacer plates. Volume fraction of high compressive strain ( &gt; 3000 microstrain) was below 5% in all experiments and no significant difference between implants was detected. Maximum vertical micromotion between bone segments was below 200 μm in all experiments and significantly larger in the implant without a tooth. Differences between plate designs generally became apparent only at 2 BW loading. Results suggest that with compressive loading of 2 BW, long spacer plates experience the lowest implant stresses, and spacer plates (long or short) result in smaller wedge micromotion, potentially beneficial for healing. Values are sensitive to subject bone geometry, highlighting the need for subject-specific modeling. This study demonstrates the benefits of using image-based FE modeling and bone theory to fine-tune HTO implant design.

Toe-out angle changes after total knee arthroplasty in patients with varus knee osteoarthritis

Toeing-out is a commonly proposed kinematic variable that has been suggested to reduce external knee adduction moment. Analyses of the toe-out angle after total knee arthroplasty (TKA) are useful for obtaining a proper understanding of the abnormal gait caused by varus knee osteoarthritis (OA), as well as performing rehabilitation after arthroplasty. Changes in the toe-out angle after arthroplasty have not yet been defined or analysed. The study population consisted of 32 knees in 32 patients with varus knee OA who underwent TKA. The femorotibial angle was evaluated on standing anteroposterior radiographs before and after arthroplasty. The subjects underwent three-dimensional motion capture analyses to measure gait parameters (walking speed, cadence, stride length, step length, step width and the relative length of the single-limb support (SLS) percentage of one gait cycle) and the maximal hip adduction angle in the stance phase, the trunk lean angle in the coronal plane and the toe-out angle before and 4 weeks after arthroplasty. The femorotibial angle on the side of arthroplasty improved after surgery. Among the measured gait parameters, only the SLS percentage increased significantly. The hip adduction angle and toe-out angle on the side of arthroplasty increased significantly after surgery. The knee alignment and hip adduction angle in the coronal plane and SLS phase were normalized after arthroplasty. The increase in the toe-out angle after arthroplasty may be attributable to the restoration of a normal knee alignment. These findings contribute to obtaining a proper understanding of the abnormal gait caused by varus knee OA and are useful for orthopaedic surgeons and rehabilitation therapists when treating patients after arthroplasty. Prospective study, Level II.

Is valgus unloader bracing effective in normally aligned individuals: implications for post-surgical protocols following cartilage restoration procedures

Utilizing valgus unloader braces to reduce medial compartment loading in patients undergoing cartilage restoration procedures may be an alternative to non-weightbearing post-operative protocols in these patients. It was hypothesized that valgus unloader braces will reduce knee adduction moment during the stance phase in healthy subjects with normal knee alignment. Gait analysis was performed on twelve adult subjects with normal knee alignment and no history of knee pathology. Subjects were fitted with an off-the-shelf adjustable valgus unloader brace and tested under five conditions: one with no brace and four with increasing valgus force applied by the brace. Frontal and sagittal plane knee angles and external moments were calculated during stance via inverse dynamics. Analyses of variance were used to assess the effect of the brace conditions on frontal and sagittal plane joint angles and moments. With increasing tension in the brace, peak frontal plane knee angle during stance shifted from 1.6° ± 4.2° varus without the brace to 4.1° ± 3.6° valgus with maximum brace tension (P = 0.02 compared with the no brace condition). Peak knee adduction moment and knee adduction impulse decreased with increasing brace tension (main effect of brace, P < 0.001). Gait velocity and sagittal plane knee biomechanics were minimally affected. The use of these braces following a cartilage restoration procedure may provide adequate protection of the repair site without limiting the patient's mobility.

Wear of Polyethylene Against Oxidized Zirconium Femoral Components: Effect of Aggressive Kinematic Conditions and Malalignment in Total Knee Arthroplasty

Metallic femoral components with ceramic articulating surfaces can substantially lower polyethylene (PE) wear during walking activities under conditions of normal knee alignment. It is unknown whether these types of components can maintain low wear rates under conditions of knee malalignment and the harsher kinematics associated with younger, athletically active patients. Wear was measured in non–cross-linked, ethylene oxide–sterilized PE inserts against oxidized zirconium or cobalt-chrome femoral components in a knee wear simulator. The vertical load was modified to replicate knee varus malalignment of 3°, and the range of tibial rotation was increased to 20°. Mean gravimetric and volumetric wear rate over 5 million cycles was 55% lower in the oxidized zirconium group. An oxidized zirconium femoral component can significantly reduce PE wear under simulated conditions of athletically active patients with modestly malaligned total knee arthroplasty prostheses.

Treatment of Full-Thickness Chondral Defects with Hyalograft C in the Knee

Background Tissue engineering has become available for cartilage repair in clinical practice. Hypothesis The treatment of full-thickness chondral defects in the knee with a hyaluronan-based scaffold seeded with autolo-gous chondrocytes provides stable improvement of clinical outcome up to 7 years. Study Design Case series; Level of evidence, 4. Methods Fifty-three patients with deep osteochondral defects in the knee were treated with Hyalograft C. The mean age at implantation was 32 6 12 years, the mean defect size was 4.4 6 1.9 cm2, and the mean body mass index was 24.5 6 3.8 kg/m2. Implantations were performed with miniarthrotomy or arthroscopy. The primary indications for implantation with Hyalograft C included young patients with a stable joint, normal knee alignment, and isolated chondral defects with otherwise healthy adjacent cartilage. The secondary indications were patients who did not meet the primary indication criteria or were salvage procedures. Forty-two patients with primary indications and 11 patients with secondary indications were evaluated. Outcome was evaluated with the International Cartilage Repair Society and International Knee Documentation Committee scales, the Lysholm score, the modified Cincinnati score, and with Kaplan-Meier survival analysis. Statistical analysis consisted of bivariate correlation analysis and unpaired, 2-tailed t tests. Results A highly significant increase (P<001) in all knee scores was found in patients treated for the primary indications. Nine of 11 secondary indication cases underwent total knee arthroplasty due to persisting pain between 2 and 5 years after implantation. Graft failure occurred in 3 of 42 patients with primary indication between 6 months and 5 years after implantation. Kaplan-Meier survival demonstrated significantly different chances for survival between primary and secondary outcome and between simple, complex, and salvage cases, respectively (P <.001). Conclusion Hyalograft C autograft provides clinical improvement in healthy young patients with single cartilage defects. Less complicated surgery and lower morbidity are considered advantages of the technique. The results of treatment with Hyalograft C as a salvage procedure or in patients with osteoarthritis are poor.

Allogene Meniskustransplantation

Loss of meniscal cartilage leads to degenerative arthritis. Therefore, it is important to save the meniscus whenever possible. But not all damaged menisci can be treated by partial resection or repair. The concept of meniscal transplantation has been suggested and has been become more common in recent years. Meniscal transplantation should be considered for the young patient who has not developed advanced osteoarthritis. Ligament stability and normal knee alignment are further requirements for meniscal transplantation. At this time, meniscal allografts provide the best a priori conditions to prevent degenerative arthritis, but the use of allografts includes the risk of disease transmission. Open and arthroscopically assisted techniques have been described. Correct size matching and positioning as well as secure fixation of the meniscal horn are important for successful meniscal allograft transplantation. Even though controlled clinical studies have not yet provided clear evidence that meniscal transplantation prevents degenerative arthritis, pain relief and functional improvement have been found in follow-up studies.

Meniscal Allograft Transplantation

Meniscal transplantation has become an accepted treatment option for selected symptomatic patients who have undergone a complete or near-complete meniscectomy. Basic and preliminary clinical studies suggest a meniscal allograft may replicate (though not completely) the shock-absorbing function of the normal meniscus to alleviate pain and provide measurable improvement in knee function. However, there is limited information on which to base crucial clinical decisions in treating the meniscectomized patient. I systematically explored available literature to address four general questions: Who is the ideal patient for a meniscal transplantation? What is the ideal method of graft sizing, preservation, and implantation? What is the accepted means of postoperative rehabilitation and timing of a return to athletic activities? And finally, what is the overall success rate of this procedure? This review of existing clinical trials revealed several crucial treatment principles for surgeons performing this procedure: (1) achieving or reestablishing normal knee alignment and stability; (2) implanting a size-matched, non-irradiated graft with secure fixation of the meniscal horns; and (3) ensuring patients return only to light sports activities to maximize the chances for graft survival. By following these principles, symptomatic improvement can be achieved in the majority of patients.

FOOT INJURY - SOCCER

1165 HISTORY - An 18 year-old white female, Division I soccer player complained of chronic right second toe pain. The pain began approximately six months earlier. She only remembered an injury of another player stepping on her foot in the past. She initially was treated just for a contusion, but had continued pain. She continued to have problems to the point she was unable to play soccer. PHYSICAL EXAMINATION - She had normal knee alignment and mild asymptomatic hallux valgus and 4° hindfoot varus on the right. She had no Achilles tightness. She was tender directly over the second metatarsal head and neck. She had pain with plantar flexion of the MTP joint, as well as pain with passive dorsiflexion. She had no pain at the base of the second metatarsal, but some pain around the neck of the second metatarsal. She had an increased drawer sign at the second MTP joint with increased translation and mild pain at the 2-3 interdigital nerve area. She had normal sensation, normal pulses, and a negative straight leg raise. 2nd metatarsal neck fracture 2nd MTP instability 2-3 interdigital neuroma Plantar plate injury 2nd MTP joint Chondral injury 2nd metatarsal head Freiberg's infarction TEST AND RESULTS: initially read as negative with no obvious stress fracture, normal alignment question of mild increased density to the 2nd metatarsal head no definite Freiberg's infarction Bone scan - uptake at 2nd metatarsal head and neck area MRI - read as negative FINAL/WORKING DIAGNOSIS: 2nd MTP instability vs. chondral lesion of the 2nd metatarsal head Extended steel shank, 2nd toe taping for instability with persistent pain. Exploration of 2nd metatarsal head with noted synovitis and chondral avulsion injury to 2nd metatarsal head. Debridement of chondral lesion and subchondral bone drilling. Taping of toe, post-op shoe, early active and passive ROM exercises. Biking at 1 week post-op, Stairmaster at 4 weeks, running at 6 weeks, return to soccer 2 1/2 months post -op with minimal to no pain.

New horizons in the treatment of osteoarthritis of the knee.

OSTEOARTHRITIS IS NOT SIMPLY A degenerative disorder. Rather, it is a complex derangement of articular surfaces that involves the loss of normal collagen architecture followed by an attempt by chondrocytes to produce replacement cartilage. The replacement surface is less resistant to wear than the original. Over time, fullthickness cartilage loss may develop on the articular surfaces. Symptoms of osteoarthritis include joint pain, typically worse with use and eased with rest, and joint stiffness after nonuse. The pain can become persistent. In the past, failure of symptomatic treatment, such as nonsteroidal anti-inflammatory drugs and physical therapy, has left joint replacement as the principal option in the care of more severely affected patients. However, in recent years, 3 new intra-articular procedures have shown promise for some patients with articular cartilage defects of the knee. Multiyear follow-up has shown encouraging results for these treatments of diffuse osteoarthritis and focal articular defects of the knee. Focal articular cartilage defects, often found in young adults, have been increasingly recognized as a cause of functional problems. To date, only lesions on the femoral condyles and trochlear groove have been effectively treated. Two techniques to treat these lesions, autogenous cartilage implantation (ACI) and autogenous osteochondral grafting, improved knee function in 2to 5-year follow-ups in carefully selected patients. Patients most likely to benefit are those with normal knee alignment, no evidence of ligamentous instability, and no evidence of arthritis on the corresponding tibial surface. In general, the radiographs of these patients’ knees are normal or near normal, with little evidence of joint space narrowing or osteophyte formation in weight-bearing radiographs. For the more common condition of diffuse osteoarthritis of the knee, the Food and Drug Administration has approved the intra-articular injection of forms of hyaluronic acid in more advanced cases. Technically classified as a device rather than a drug, hyaluronic acid compound injection has been used outside the United States, with functional improvement in up to 77% of patients.