The association of frontal plane alignment to MRI-defined worsening of patellofemoral osteoarthritis: the MOST study.

OBJECTIVE: To determine the sex-specific relation of frontal plane alignment (FPA) to magnetic resonance imaging (MRI)-defined features of patellofemoral osteoarthritis, and also to tibiofemoral osteoarthritis and knee pain. METHOD: The Multicenter Osteoarthritis Study is cohort study comprised of individuals with or at risk of knee osteoarthritis. We determined the sex-specific dose-response relation of baseline FPA to MRI-defined patellofemoral and tibiofemoral structural worsening, and incident knee pain, over 7 years. RESULTS: In women only, greater varus alignment was associated with medial patellofemoral osteophytes (risk ratio [RR] 1.7 [95% CI 1.2, 2.6]) and valgus with lateral patellofemoral osteophytes (RR 1.9 [1.0, 3.6]). In men, greater varus increased risk for medial tibiofemoral cartilage worsening (RR 1.7 [1.1, 2.6]), and valgus for lateral tibiofemoral cartilage worsening (RR 1.8 [1.6, 2.2]). In women, findings were similar for tibiofemoral cartilage, but varus also increased risk for medial bone marrow lesions [BMLs] (RR 2.2 [1.6, 3.1]) and medial osteophytes (RR 1.8 [1.3, 2.5]), and valgus for lateral BMLs (RR 3.3 [2.2, 4.5]) and osteophytes (RR 2.0 [1.2, 3.2]). Varus increased risk of incident pain in men (RR 1.7 [1.4, 2.2]) and women (RR 1.3 [1.0, 1.6]), valgus did so in men only (RR 1.5 [1.1, 1.9]). CONCLUSION: FPA was associated with patellofemoral osteophyte worsening in women, though overall was more strongly associated with tibiofemoral than patellofemoral osteoarthritis feature worsening. FPA in women was more consistently associated with structural worsening, yet men had higher associations with incident pain.

Validity and sensitivity to change of three scales for the radiographic assessment of knee osteoarthritis using images from the Multicenter Osteoarthritis Study (MOST).

OBJECTIVES: The purpose of this study was to assess the concurrent validity and sensitivity to change of three knee osteoarthritis (OA) grading scales. The Kellgren-Lawrence (KL) and the Osteoarthritis Research Society International (OARSI) joint space narrowing (JSN) grading scales are well-established. The third scale, the compartmental grading scale for OA (CG) is a novel scale which grades JSN, femoral osteophytes, tibial erosion and subluxation to create a total score. METHODS: One sample of 72 posteroanterior (PA) fixed-flexion radiographs displaying mild to moderate knee OA was selected from the Multicenter Osteoarthritis Study (MOST) to study validity. A second sample of 75 radiograph pairs, which showed an increase in OA severity over 30 months, was selected to study sensitivity to change. The three radiographic grading scales were applied to each radiograph in both samples. Spearman's rank correlation coefficients were used to correlate the radiographic grades and the change in grades over 30 months with a Whole-organ Magnetic Resonance Imaging Score (WORMS)-based composite score which included five articular features of knee OA. RESULTS: Correlations between the KL, OARSI JSN and CG grading scales and the magnetic resonance image (MRI)-based score were 0.836, 0.840 and 0.773 (P < 0.0001) respectively while correlations between change in the radiographic grading scales and change in the MRI-based score were 0.501, 0.525 and 0.492 (P < 0.0001). CONCLUSIONS: All three radiographic grading scales showed high validity and are suitable to assess knee OA severity. They showed moderate sensitivity to change; therefore caution should be taken when using ordinal radiographic grading scales to monitor knee OA over time.

Standardized standing pelvis-to-floor photographs for the assessment of lower-extremity alignment.

OBJECTIVES: The objective of this cross-sectional study was to assess the intra-rater, inter-rater and test-retest reliability and concurrent validity of lower-extremity alignment estimated from a photograph [photographic alignment (PA) angle]. METHODS: A convenience sample of participants was recruited from the community. Radiopaque stickers were placed over participants' anterior superior iliac spines. One radiograph and one photograph were taken with the participant standing in a standardized position. The stickers were removed. After 30 min they were reapplied and a second photograph was taken. The hip-knee-ankle (HKA) angle was measured from each radiograph using customized imaging analysis software. The same software was used by three readers to measure the PA angle from each photograph from the first set twice, at least 2 weeks apart. One reader measured the PA angle from the second set of photographs. Reliability was tested using intraclass correlation coefficients (ICC(2,1)), Bland-Altman analyses and the minimal detectable change (MDC95). Concurrent validity was tested using a Pearson's correlation coefficient and Bland-Altman analysis. RESULTS: Fifty adults participated (mean age 41.8 years; mean body mass index 24.7 kg/m(2)). The PA angle was 4.5° more varus than the HKA angle; these measures were highly correlated (r = 0.92). Intra-rater (ICC(2,1) > 0.985), inter-rater (ICC(2,1) = 0.988) and test-retest reliability (ICC(2,1) = 0.903) showed negligible bias (<0.20°). The MDC95 was 2.69°. CONCLUSIONS: The PA angle may be used in place of the HKA angle if a bias of 4.5° is added. A difference of 3° between baseline and follow-up would be considered a true difference.

Does measurement of the anatomic axis consistently predict hip-knee-ankle angle (HKA) for knee alignment studies in osteoarthritis? Analysis of long limb radiographs from the multicenter osteoarthritis (MOST) study.

OBJECTIVE: Researchers commonly use the femoral shaft-tibial shaft angle (FS-TS) from knee radiographs to estimate the hip-knee-ankle angle (HKA) in studies examining risk factors for knee osteoarthritis (OA) incidence and progression. The objective of this study was to determine the relationship between HKA and FS-TS, depending on the method of calculating FS-TS and the direction and degree of knee deformity. METHODS: 120 full-length digital radiographs were assigned, with 30 in each of four alignment groups (0.0°-4.9°, and ≥5.0° of varus and valgus), from a large cohort of persons with and at risk of knee OA. HKA and five measures of FS-TS (using progressively shorter shaft lengths) were obtained using Horizons Analysis Software, Orthopaedic Alignment & Imaging Systems Inc. (OAISYS). The offsets between HKA and the different versions of FS-TS were calculated, with 95% confidence intervals (CIs). Pearson correlations were calculated. RESULTS: In varus limbs use of a shorter shaft length increased the offset between HKA and FS-TS from 5.1° to 7.0°. The opposite occurred with valgus limbs (from 5.0° to 3.7°). Correlations between HKA and FS-TS for the whole sample of 120 individuals were excellent (r range 1.00-0.88). However, correlations for individual alignment groups were low to moderate, especially for the shortest-shaft FS-TS (r range 0.41-0.66). CONCLUSIONS: The offsets obtained using the shorter FS-TS measurements vary depending on direction and degree of knee deformity, and therefore may not provide reliable predictions for HKA We recommend that full-length radiographs be used whenever an accurate estimation of HKA is required, although broad categories of alignment can be estimated with FS-TS.

Can anatomic alignment measured from a knee radiograph substitute for mechanical alignment from full limb films?

OBJECTIVES: To examine whether categories of anatomic alignment (varus, neutral, valgus) measured from knee X-rays agree with similar categories of mechanical alignment from the full limb film and whether varus anatomic malalignment predicts medial joint space loss on knee X-rays as well as varus mechanical alignment. METHODS: We used data from the Osteoarthritis Initiative (OAI) (full limb and flexed knee X-rays) to examine agreement of anatomic and mechanical alignment and data from Boston Osteoarthritis of the Knee Study (BOKS) to evaluate the association of full limb mechanical alignment vs knee X-ray anatomic alignment with joint space loss. A 4 degree offset was used to correct for the more valgus angulation of the anatomic alignment. RESULTS: Of 143 subjects whose knee X-rays and full limb films were publicly released from the OAI, the agreement of varus, neutral and valgus alignment was only moderate (kappa=0.43, P<0.001). In BOKS, varus mechanical and anatomic alignments measured from full limb and knee X-rays respectively both predicted a high risk of medial joint space loss vs neutral alignment--for mechanical alignment, odds ratio (OR)=4.82 [95% confidence interval (CI) 1.93, 12.00] and for anatomic alignment OR=4.25 (95% CI 2.08, 8.72). CONCLUSIONS: While agreement of alignment from knee X-ray to full limb film was only moderate, varus malalignment measured from a flexed knee predicted the likelihood of progression well. Flexed knee alignment may be more relevant to knee osteoarthritis (OA) risk than that of a fully extended knee, but a measurement of alignment from a short limb is an imperfect surrogate for full limb alignment.

Ochronotic arthropathy: case report and review of the literature.

Alkoptonuria is an inherited metabolic disorder which is associated with various systemic abnormalities and related to the deposition of homogentisic acid pigment in connective tissues. These pigmentary changes are termed "ochronosis". We describe two patients with ochronotic arthropathy who presented with progressive and advanced degenerative changes in the lumbo-sacral spine. The literature, differential diagnosis and management of this rare condition are reviewed in this article. Management is usually conservative, but replacement surgery may be offered for severely affected major joints.

Kinematics of the knee joint in deep flexion: a radiographic assessment.

The purpose of this study is to describe the kinematics of normal knees in vivo, assessed in deep flexion, using bi-planar radiographs. Antero-posterior and lateral views were obtained from five healthy males during three sequential positions of kneeling. In the first position, the subject knelt with the knees fully flexed (deep flexion between 150 and 165 degrees) and torso upright. In the second position, the subject bowed forward to an intermediate position (about 120 degrees of knee flexion). In the third position, the subject bowed further until his head touched the floor, supporting the upper torso with hands and with the knees flexed at about 90 degrees. The results show that past 135 degrees of knee flexion, the patella cleared the femoral groove and was in contact only with the condyles. For these particular postures, and during deep flexion, motion of the femur on the tibia did not reveal the classical femoral 'roll back'. Rather the lateral femoral condyle rolled further over the postero medial aspect of the lateral tibial plateau while contact of the medial femoral condyle occurred more anteriorly, but still in the posterior part of the medial plateau. This asymmetric rolling motion indicated an element of internal tibial rotation. Furthermore, the tibia was found to articulate with the femur at the most proximal points of the condyles in deep flexion. These data on the kinematics and contact characteristics of the tibio-femoral joint must be considered in any approach to design for a Deep Flexion Knee Implant.

Knee kinematics in-vivo of kneeling in deep flexion examined by bi-planar radiographs.

Squatting and kneeling are important daily activities for Middle and Far East cultures that require positioning the knee in deep flexion. In these activities, the limb becomes fully flexed with a knee flexion angle reaching between 150 and 160 degrees and the heel reaching the posterior surface of the upper thigh. Existing knee prostheses do not allow a full return to normal activities for this large population since they are limited to achieving knee flexion of about 120 degrees. Also, there is very limited information on knee kinematics and/or forces in the range beyond 120 degrees. The purpose of this study is to describe the kinematics of normal knees in-vivo, assessed in deep flexion, using bi-planar radiographs. A-P and lateral views were obtained from 5 healthy subjects during three sequential positions of kneeling. In the 1st position, the subject knelt with the knees fully flexed (deep flexion between 150 degrees and 160 degrees) and torso upright. In the 2nd position, the subject bowed forward to an intermediate position (about 120 degrees of knee flexion). In the 3rd position, the subject bowed further until his/her head touched the floor, supporting the upper torso with hands and attaining a knee flexion of about 90 degrees. The results show that past 135 degrees of knee flexion, the patella was found to clear the femoral groove and was in contact only with the condyles. The results also show that the classical femoral "roll back" does not appear to occur in deep flexion. It seems that the lateral femoral condyle rolls over the postero medial aspect of the lateral tibial plateau while contact of the medial femoral condyle occurs more anteriorly, but still in the posterior aspect of the medial tibial plateau. This asymmetric rolling motion implies an element of internal tibial rotation. Furthermore, the tibia was found to articulate with the femur at the most proximal points of the condyles in deep flexion. These data on the kinematics and contact characteristics of the tibio-femoral joint must be considered in any approach to design for a Deep Flexion Knee Implant.

Trabecular microstructure in the medial condyle of the proximal tibia of patients with knee osteoarthritis.

The microstructural characteristics of osteoarthritic subchondral bone in the medial tibial condyle are clearly different from normal age-matched bone. Subchondral sclerosis in osteoarthritis indicates not only an increase in bone volume fraction but also alteration in other microstructural characteristics. Eleven medial tibial condyles were collected from ten subjects during arthroplastic surgery for knee oseoarthritis. They were compared to four medial tibial condyles from four age-matched controls with no history of any bone or joint disorder. Six sections from anterior to posterior and three levels from proximal to distal were evaluated in each medial condyle. Five histomorphometric parameters were measured: bone volume fraction (BVf), trabecular thickness (Tb.Th), trabecular number (Tb.N), trabecular separation (Tb.S), and trabecular connectivity (Tb.C). In general, the osteoarthritic subchondral bone had a higher bone volume fraction than control bone but the microstructure was characterized by fewer, widely spaced, thicker than normal trabeculae. There were also highly localized regional differences by depth from the articular surface and from anterior to posterior across the medial condyle. These variations in OA subchondral bone microstructure may significantly affect biomechanical competence of bone in a way not predictable by bone volume fraction measurements alone.

Changes in mean trabecular orientation in the medial condyle of the proximal tibia in osteoarthritis.

In osteoarthritis of the knee, degenerative changes occur in the articular cartilage and underlying subchondral bone, particularly of the medial tibial condyle. Cancellous bone sclerosis that accompanies osteoarthritis is not only the result of an increase in bone volume fraction but also a change in trabecular structure. In a comparison with age-matched controls (n = 4), osteoarthritis (n = 11) demonstrated a significant (P < or = 0.05) increase in bone volume fraction and trabecular thickness. Overall trabecular orientation in the osteoarthritic group was more vertical or perpendicular to the articular surface than the control group (P < or = 0.05) especially in the trabeculae of the cancellous bone layer closest to the articular surface. These alterations in trabecular bone structure could have significant consequences for the mechanical properties of osteoarthritic bone.

A quantitative technique for reporting surface degradation patterns of UHMWPE components of retrieved total knee replacements.

A quantitative method of reporting surface degradation of the ultra-high molecular weight polyethylene (UHMWPE) tibial component from retrieved total knee replacements (TKR) was developed. Specific features include a qualitative assessment expressing the patterns in which the damage was detected as well as a quantitative summary of the observed degradation mechanisms. In addition, a method of measuring lower limb alignment changes with time is described and related to the observed damage patterns. Two case studies are presented. One case illustrated that changes in alignment resulted from factors other than wear. The damage observed on the tibial plateau appeared to occur subsequent to the changes in alignment. The second case illustrated that the wear of the UHMWPE tibial insert lead to the changes in the overall lower limb alignment. The methods described provide additional information regarding TKR failure mechanisms compared to reporting methods currently available. In particular, the collection of temporal alignment data at clinical follow-up visits enhanced the assessment of the retrieved TKR.

Patterns of knee arthrosis and patellar subluxation.

This study was based on the unexpected observation of lateral patellofemoral subluxation in the varus osteoarthritic knee. Standardized radiographs of 109 knees (65 patients with osteoarthritis) were selected randomly from the authors' database and retrospectively reviewed. Hip-knee-ankle alignment data were correlated with patellofemoral subluxation and tilt, as well as with radiographic patellofemoral grades for arthrosis. The amount and site of patellofemoral arthrosis were correlated with patellar position and limb alignment. Patellae that were located centrally in the trochlear groove had the lowest radiographic score for arthrosis. Subluxation of the patella, either medially or laterally, was correlated with increased radiographic scores. Limb alignment was not correlated with the radiographic score. A significant percentage of varus knees (28%) had unexpected lateral subluxation of the patella. This observation has not been reported previously. It may have an impact on surgical decision-making for total knee arthroplasty and osteotomy.

Studies of thrombin-induced proteoglycan release in the degradation of human and bovine cartilage.

Because fibrin is commonly observed within arthritic joints, studies were undertaken to determine whether purified coagulation and fibrinolytic proteases degrade cartilage in vitro and to seek evidence for the activation of coagulation in arthritic joints through measurements of the levels of inhibitor-enzyme complexes and several other proteins associated with coagulation and fibrinolysis. The concentrations of 13 plasma proteins and complexes of thrombin and Factor Xa with antithrombin III were measured in synovial fluids recovered at the time of knee replacement surgery. All zymogens necessary to constitute the coagulation cascade were present. Thrombin and the combination of prothrombin plus prothrombinase induced proteoglycan release from both normal and arthritic cartilages. Factor Xa and plasmin induced release from diseased cartilage only, and urokinase, tissue plasminogen activator, and activated protein C were without effect at the levels used. At saturating levels of thrombin (> or = 2.0 microM) 80% of the proteoglycan content of normal cartilage was released within 24 h. Thrombin, which is cationic, reversibly binds cartilage with Kd = 7.0 +/- 1.0 microM and Bmax = 820 +/- 70 ng/mg of human cartilage. Levels of thrombin-antithrombin III complexes in synovial fluids and arthritis were 4-fold higher in osteo (OA) and 43-fold higher in rheumatoid (RA) than in controls (0.98 nM). Factor Xa-antithrombin III complex levels were threefold lower in OA and fivefold higher in RA than in controls (0.24 nM). These elevated levels of enzyme-inhibitor complexes imply a history of activation of coagulation within the joint, especially in RA. Since thrombin degrades cartilage in vitro and had been generated in vivo, as inferred by the existence of thrombin-antithrombin III complexes, intraarticular activation of coagulation may both contribute to the pathology of arthritis and comprise a target for therapy and diagnosis.

Radiographic assessment of bony contributions to knee deformity.

Our recommendations for standing radiography of the lower limb are that assessments be standardized with respect to limb rotation and fixed relative positions of the hip, knee, and ankle. Specifically, a neutral knee rotation position should be set up, defined as alignment of the flexion plane straight ahead. For a complete appraisal, there should be both AP and lateral views in which the positioning of the patient is the same in all respects. The QPR frame greatly assists in achieving these objectives. Furthermore, the presence of a calibration system adds to the reliability and reproducibility of data by compensating for errors of position or alignment arising from the placement of the source and the film. Standardization of positioning also improves the detectability of axial-rotational deformities on comparison of AP and lateral views, providing more reliable indications of the need for CT than possible with nonstandardized short views. When a skyline patellar radiograph is added to the QPR routine, the end result is an excellent appraisal of lower limb alignment, providing a solid basis for diagnosis and planning of appropriate surgical remedies.

Bone strength and histomorphometry of the distal femur.

The ultimate bone strength of the distal femur was measured radially, by indentation testing, around the transepicondylar line in 3 mm depth steps up to 12 mm below the subchondral bone plate. Specimens from 10 cadavers were used. This orientation of specimens was chosen as a way to provide measurement in a more physiologic orientation for load bearing and to standardize the assessment. Bone hardness declined sharply over the first 6 mm below the surface, tending to plateau at deeper levels. Within the top 6 mm layer the lateral condyle was softer than both the medial condyle and the central patellofemoral area (P < .05), but at deeper levels it maintained greater hardness. Of the histomorphometric parameters, those showing the greatest consistent correlation with hardness were bone volume fraction and trabecular separation. When the tibiofemoral and patellofemoral compartments were compared it was found that for a given value of bone volume fraction, condylar bone is marginally harder than patellofemoral bone. The data are relevant to the design of implants that match their geometric and material properties to the shape and strength of the underlying bone.