Knee osteoarthritis following ACL injuries

                                    Knee osteoarthritis following ACL injuries

                                                                  Dr KS Dhillon

Introduction

Anterior cruciate injuries are common and annual incidence in the general population is high. Large numbers of ACL reconstructions are carried out annually around the world. It is well known that knee osteoarthritis (OA) often develops after ACL injury. However the reported incidence of OA after ACL injuries, in literature, varies widely. Though OA is a common disease there remains no consensus in literature on the criteria for diagnosis of OA.

Diagnosis of knee osteoarthritis

Despite the extensive research in this field of medicine there is still lack of consensus regarding the criteria for the diagnosis of osteoarthritis (OA). Altman et al [1] in 1986 proposed the following criteria for the diagnosis of knee OA:

American College of Rheumatology criteria for classification of idiopathic osteoarthritis (OA) of the knee.

A. Clinical Clinical and laboratory

Knee pain and at least 5 of the following 9

• Age >50 years
• Stiffness <30 minutes
• Crepitus
• Bony tenderness
• Bony enlargement
• No palpable warmth
• ESR <40 mm/hour
• RF <1:40
• SF OA

(ESR = erythrocyte sedimentation rate (Westergren); RF = rheumatoid factor; SF OA = synovial fluid signs of OA (clear, viscous, or white blood cell count <2000/mm).


B.Clinical and radiological
Knee pain and osteophytes and 1 of the 3

• Age >50 years
• Stiffness <30 minutes
• Crepitus

C.Clinical
Knee pain with 3 of the 6

• Age >50 years
• Stiffness <30 minutes
• Crepitus
• Bony tenderness
• Bony enlargement
• No palpable warmth

However there has been some criticism of this criteria for diagnosis of OA of the knee [2].

Radiological diagnosis of OA

One of the widely used classification of radiological OA is that by Kellgren and Lawrence (K-L) [3].
There are 5 grades of OA in this classification;

• Grade 0---No OA
• Grade 1---Doubtful OA
• Grade 2---Minimal OA
• Grade 3---Moderate OA
• Grade 4---Severe OA

Although this classification is frequently used, there has been criticism about its usefulness. For instance there are several versions of this classification in use [4], and the cutoff grade for defining OA is osteophytes and not joint space narrowing. There are other classifications which are also used for classification of radiographic OA and they include the Osteoarthritis Research Society International (OARSI) atlas [5], the Ahlbäck classification [6], and the IKDC classification [7].The cutoff for defining knee OA in these classifications includes JSN of about 50% (2- 4mm).

Standing and semiflexed standing views of the knee are recommended for radiographic assessment of OA. Buckland Wright et al [8] evaluated different positions and found that the semi flexed position gave the best x-rays for evaluation of knee OA. In the semiflexed view the site of measurement is at the middle of the tibial plateau, consistent with the region of normal functional loading of the knee. Osteophytes formation, joint space narrowing (JSN), sclerosis, and bone deformations are the structural changes examined on these x rays[6].

Etiology of OA after ACL injury

It is well know that ACL injuries cause OA of the knee but the exact mechanism how such injuries cause OA is not fully understood [9]. Studies however have suggested that there is increased loading of the joint after ACL injury due to quadriceps weakness. Both the quadricep weakness and tear of ACL contributes to decreased dynamic knee joint stability which leads to OA [10,11]. The quadriceps muscle has an efficient shock absorbing ability when the knee joint is loaded during upraised activities.

When the muscles become weak this ability to absorb shock is reduced which increases the stresses at the articular surface leading to microdamage in the cartilage [12].
It has been suggested that the mechanism responsible for quadriceps weakness after ACL injury is inactivity atrophy and/or arthrogenic muscle inhibition (AMI) [13, 10]. Some studies have suggested that quadriceps weakness appears to be a risk factor for the initiation of knee OA[14].

Beside muscle weakness there are other risk factors which influence the development of knee OA following an ACL injury and these include increased age at the time of the injury, additional meniscal tears with subsequent meniscectomy, chondral lesions, and ACL reconstruction with BPTB graft [15].

Incidence of OA following ACL injuries

Knee ligament laxity is a well known risk factor for posttraumatic osteoarthritis (PTOA). The incidence of radiographic PTOA after Anterior cruciate ligament (ACL) injuries has been reported in 16% to 90% of individual at between 5 to 15 years after the injury [16].

Lohmander et al [17] reported an average of 50% incidence of PTOA at 10 to 20 years after the diagnosis of a tear of the ACL or a tear of the meniscus. The OA is associated with pain and functional impairment. They described it as ‘the young patient with an old knee’.
Wilder et al [18] in a prospective epidemiological assessment of men and women aged 40 years and older found that individuals with history of acute knee injury were 7.4 times more likely to develop OA of the knee as compared to those with no history of knee injury.

Lohmander et al [19] followed up a cohort of 26–40 year old female soccer players who had sustained an ACL injury 12 years earlier. They found an incidence of slightly more than 50% of radiographic OA in the injured knee and about 80% had a radiographic feature related to OA (JSN or osteophyte OARSI grade ≥1). Seventy five percent of the 84 women had knee symptoms which substantially affected their knee-related QOL, and 28 subjects (42%) were defined as having symptomatic radiographic knee OA.

von Porat et al [20] at 14 years follow up of 219 male soccer players with an ACL injury, found radiographic changes in 78% of the injured knees. Kellgren-Lawrence grade 2 or higher changes were seen in 41% of the injured knees and 4% had Kellgren-Lawrence grade 2 or higher radiographic changes in the uninjured knee.They found no difference between surgically and conservatively treated players.

McDaniel Jr and Dameron Jr. [21] followed up forty-nine patients (52 knees) with untreated anterior cruciate ligament (ACL) ruptures for an average of 14 years. Eighty-six percent of the knees had one or both menisci removed. One-third of the knees demonstrated joint space narrowing or unequivocal evidence of osteoarthritis.

 Kannus and Järvinen [22] followed up 77 patients with partial or complete tears of the ACL for an average of 8 years. They found that 70% of the patients with complete and 14% of patients with partial tear developed OA of the injured knee.
Segawa et al [23] retrospectively reviewed the records of 89 patients with tear of the ACL  who were treated nonoperatively. The average age of the patients was 34.9 years and the mean follow up period was 12 years. Sixty three percent of the patients had evidence of OA and 37% there was joint space narrowing.

Sommerlath et [24] in a 9 to 16 years follow up of patients with a torn ACL found an incidence of OA in 58% of patient below the age of 35 years and an incidence of 87% in older patients.
Other authors have found a higher incidence of OA in patients with ACL reconstruction as compared to those who had no reconstruction [25,26].

However some authors have reported a much lower incidence of tibio-femoral OA after conservative treatment of ACL injuries. Neuman et al [27] reported a low occurrence of tibiofemoral OA and good knee function in patients treated without ACL reconstruction. They followed up 100 consecutive patients with an acute, complete ACL injury for 15 years. All patients were primarily treated with activity modification and supervised physical therapy without ACL reconstruction.Sixteen percent of the patient with ACL injury developed OA and all these patients had meniscectomy in addition to the ACL injury. None of the other patients who did not have a meniscectomy developed OA of the knee. Sixty eight percent of the patients had an asymptomatic knee. Twenty-three percent of the patients underwent ACL reconstruction with a mean time of 4 years after injury.

Neuman et al [16] also found a low incidence of patellofemoral OA in patients with ACL tear who were treated conservatively as compared to those who were treated with an ACL reconstruction using the patella tendon graft.They found an incidence of 16% OA of the patello-femoral joint at 15 years follow up in patients treated conservative for ACL injuries. None of the knees had joint space narrowing and there were only grade 1 and grade 2 osteophytes in the knees of patients with OA.

OA after ACL reconstruction

Reports of incidence of OA after ACL reconstruction in literature varies widely. Hoffelner et al [28] followed up 28 patients with isolated ACL tears without concomitant injuries, who had ACL reconstruction, for an average of 10 years. They found no statistical difference in the incidence of OA (K-L) and function between the injured and uninjured knees. The incidence of OA in the injured knee was 21% and in the uninjured knee 14%.

Gerhard et al [29] reviewed 63 patients who were treated by ACL reconstruction at a mean follow up of 16 years. The Kellgren-Lawrence score was grade 0 in 27 %, grade 1 in 40 %, grade 2 in 8%, grade 3 in 14 % and grade 4 in 5 % of the patients. Hence only 27 % of the patients had OA at 16 years follow up in patients with ACL reconstruction.

Oiestad et al [30] prospectively followed up 258 consecutive patients who had ACL reconstruction for 10-15 years to see the associations between radiographic tibiofemoral knee OA and knee pain, symptoms, function and knee-related quality of life (QOL). They found radiographic knee OA (K&L ≥ grade 2) in 71% of the patients and 24% of the patients had moderate or severe radiographic knee OA (K&L grades 3 and 4). There was no significant associations between radiographic knee OA (K&L grade ≥ 2) and pain, function or QOL but patients with severe radiographic knee OA (K&L grade 4) significantly had more pain, symptoms, impaired Sport/Rec and reduced QOL.

Oiestad et al [31] followed up patients with isolated ACL injuries and combined injuries after ACL reconstruction for 10 to 15 years. They found  significant differences in knee function over time between the isolated and combined injury groups. Patients with combined injury had significantly higher prevalence of radiographic knee osteoarthritis compared with those with isolated injury (80% and 62%, P = .008), but there was no significant group differences for symptomatic radiographic knee osteoarthritis (46% and 32%, P = .053).

Chalmers et al [32] carried out a systematic literature review of the long-term outcome (minimum follow-up, more than ten years) after ACL reconstruction and nonoperative treatment of patients with ACL injuries. They evaluated knee stability on physical examination, functional and patient-based outcomes, the need for further surgical intervention, and finally the radiographic outcomes.
They found that the patients who had surgical stabilization of the knee had fewer subsequent meniscal tears, less need for further surgery, and a greater change in activity from the preoperative level as measured with the Tegner score as compared to patients treated without surgery. However there were no significant differences in the the Lysholm score, IKDC score, and radiographic progression of OA between the two groups.

Risk of knee arthroplasty after ACL injuries

Leroux et al [33] carried out a population-based cohort study to determine the risk of knee arthroplasty ( a surrogate for end-stage osteoarthritis) in patients who had anterior cruciate ligament reconstruction. They obtained their information from administrative databases of patients who had undergone ACL reconstruction in the Ontario region from July 1993 to March 2008.
They found that after 15 years, the cumulative incidence of knee arthroplasty following cruciate ligament reconstruction was low at 1.4%.

Although the incidence was low it was however seven times greater than the cumulative incidence of knee arthroplasty among matched control patients from the general population (0.2%). Factors which increased the risk of knee arthroplasty were ‘older age, female sex, higher comorbidity, low annual volume of cruciate ligament reconstruction, and cruciate ligament reconstruction performed in a university affiliated hospital were factors that increased knee arthroplasty risk’.

Conclusion

The annual incidence of ACL injuries is high and rising worldwide and with increasing number of injuries, the numbers of ACL reconstructions carried out annually is on the rise. The association between tears of the ACL and OA of the knee is well know. Despite the extensive research there is still lack of consensus regarding the criteria for the diagnosis of osteoarthritis (OA). The commonly used criteria for diagnosis of clinical OA is that by the American College of Rheumatology. The commonly used radiological classification is the one by Kellgren and Lawrence. Other radiological classifications include that by Osteoarthritis Research Society International (OARSI), the Ahlbäck classification [6], and the IKDC classification.\

It is well know that ACL injuries cause OA of the knee but the exact mechanism how such injuries cause OA is not fully understood. Beside the knee instability produced by a torn ACL, injuries to the cartilage and meniscus also contribute to the pathogenesis of OA. The least recognised factor which contributes to the OA is the weakness of the Quadriceps which usually follows ACL injuries.
The reported incidence of radiographic PTOA after Anterior cruciate ligament (ACL) injuries varies widely and has been reported in 16% to 90% of individual at between 5 to 15 years after the injury.
Prospective epidemiological studies show that individuals with history of acute knee injury were 7.4 times more likely to develop OA of the knee as compared to those with no history of knee injury. Some authors have found a higher incidence of OA in patients with ACL reconstruction as compared to those who had no reconstruction.

Despite the high incidence of OA after ACL reconstruction the cumulative incidence of knee arthroplasty following cruciate ligament reconstruction however remains low 1.4%. The incidence of knee replacement in individuals who had no reconstruction is not known but would probably be around the same figure.

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