the joint capsule. Injuries to the patella and the surrounding soft tissue, including patellar dislocations, are a known risk factor for OA progression in this articulation (Carbone & Rodeo, 2016). Soft tissue structures Several soft tissue structures play a vital role in maintaining the stability of the knee joint during dynamic activities. In particular, the medial and lateral collateral ligaments prevent valgus and varus (abduction and adduction, respectively) motions of the knee joint in the frontal plane. In the sagittal plane, the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) provide stability in conjunction with the quadriceps and hamstring muscles. In addition to restricting motion in the Diagnosis criteria Although knee OA is a fairly common, it is important to know that it can be diagnosed by different methods. It is most commonly diagnosed by either radiographic (X-ray) images or clinical features. As a physical therapist or physical therapist assistant, it is important to understand the distinction between these two methods of diagnosis as there can be a weak relationship between radiographic OA and the symptoms a person may experience. Individuals with similar grades of radiographic OA may have dramatically different levels of joint pain, and similarly, individuals with different radiographic grades of OA may have similar symptom presentation. This distinction between diagnostic criteria is also important when interpreting the results from research studies. The method of OA diagnosis may make the results more applicable to patients with either symptomatic or structural disease and may reduce the generalizability of the findings. Radiographic diagnosis Radiographic knee OA is commonly diagnosed using the methods described by Kellgren and Lawrence many decades ago (Kellgren & Lawrence, 1957). Using this method, subjects undergo weight-bearing X-rays in which the knee is slightly flexed. Because cartilage does not absorb X-rays as they pass through, the area occupied by cartilage appears as dark areas or blank space on an X-ray film. Conversely, bone is radiopaque, meaning that it blocks the X-ray beam and appears as white
sagittal plane, the ACL and PCL also prevent abnormal rotations in the transverse plane at the tibiofemoral joint. Damage to any or all of these ligaments can dramatically alter the location of joint forces throughout the knee. Even after reconstructive surgery for ligamentous injuries, motions within the knee do not return to normal. Demanding motions like cutting (Stearns & Pollard, 2013) and jumping (Pozzi, Di Stasi, Zeni, & Barrios, 2017) show dramatic alterations in joint biomechanics and loading patterns. Therefore, the integrity of these soft tissue structures not only a plays role in normal knee function, but also can result in OA progression when injured due to persistent abnormal motion, loads, or alignment. regions on an X-ray film. Therefore, the dark space between the bones can be measured and is correlated with cartilage thickness. This area of cartilage is known as joint space width on the X-ray. As cartilage starts to deteriorate with OA progression, the joint space width will appear smaller until ultimately, there is no cartilage left on the ends of the bones. This results in an X-ray image in which the bones appear to be touching and there is no joint space width. This is how the term bone-on-bone arthritis got its name, and it is indicative of end-stage knee OA, meaning there is no cartilage left between the two articular surfaces. In this condition there is a total loss of joint space. According to the Kellgren & Lawrence method of diagnosis, the X-ray image is graded on a scale of 0 to 4. A score of 0 indicates that there is no evidence of OA within the tibiofemoral knee joint. A grade of 4 means that there are substantial degenerative changes within the joint. The grades get progressively higher as the joint space gets smaller. The grades also factor in other changes associated with knee OA, including the presence of bone spurs, also known as osteophytes, which often occur as cartilage wears away in the joint and abnormal loads between the bones develop. Because this grading scale is somewhat subjective, a grade of 2 is often used as a cutoff for definitive OA, while a grade of 1 is indicative of possible OA-related changes. Examples of a normal knee X-ray and one with substantial OA are shown in Figure 2.
Figure 2: Radiographs of Knees With and Without OA
A posterior to anterior radiograph with no evidence of osteophytes or loss of joint space is seen in image (A).
Image (B) shows knees with a more severe OA, which is evidenced by small joint space in the medial tibiofemoral compartment and large osteophytes on the femur and tibial plateau.
Note. Left: © joeyphoto/Adobe Stock. Right: © stockdevil/Adobe Stock.
Clinical diagnosis Unlike the radiographic diagnosis, which relies solely on changes to the joint structure to confirm the presence of knee OA, other diagnostic methods rely on a phwysical examination combined with patient symptoms. A clinical definition proposed by the American College of Rheumatology is widely used in clinical settings and research studies (Altman et al., 1986). According to the clinical diagnosis criteria, a patient has clinical symptoms of OA if they have knee pain most days of the prior month and at least three of the following six criteria: 1. Age >50 years. 2. Morning stiffness that lasts less than 30 minutes. 3. Crepitus during active joint motion.
4. Tenderness of the bony margins of the joint. 5. Palpable bony enlargement of the knee upon physical examination. 6. No palpable warmth of the joint. While most of the established clinical diagnostic methods for knee OA target the tibiofemoral articulation, recent studies have evaluated whether clinical diagnostic criteria are able to detect patellofemoral knee OA (Stefanik, Duncan, Felson, & Peat, 2017). Unfortunately, there was no one clinical test that was indicative of patellofemoral OA on X-ray. The presence of pain while climbing stairs had very high sensitivity (96%), but poor specificity (15%). This means that patients without pain during stair climbing likely do not have patellofemoral OA, but
EliteLearning.com/Physical-Therapy
Book Code: PTNC1023
Page 2
Powered by FlippingBook