Does Chondrocalcinosis Affect Knee Society Scores and Range of Motion After TKA?

Abstract

Background

Chondrocalcinosis is manifested by crystalline deposits of calcium commonly found during primary TKA for osteoarthritis. Its frequency among patients undergoing TKA is poorly defined, as is its influence on pain or function after TKA.

Questions/purposes

The purposes of this study are to (1) determine the prevalence of chondrocalcinosis in patients undergoing TKA for osteoarthritis; (2) evaluate the effect of chondrocalcinosis on ROM and The Knee Society scores; (3) determine if patients with chondrocalcinosis and severe synovitis who underwent synovectomy are at risk for lower postoperative Knee Society scores and less ROM; and (4) assess if chondrocalcinosis is associated with increased rates of revision surgery.

Methods

We retrospectively reviewed the medical records of 1500 primary TKAs performed by one surgeon. The minimum followup for patients was 24 months (average, 57 months; range, 24–120 months). There were 511 men and 934 women with an average age of 70 years. Fifty-five patients underwent bilateral knee replacements. Crystal deposition was graded prospectively during surgery using a subjective visual scale. A thorough synovectomy was performed on patients with severe synovitis and apparent crystalline deposition suggestive of calcium pyrophosphate dihydrate (CPPD) deposition (n = 50). The Knee Society scores, ROM, and revision rates were compared between patients with visible chondrocalcinosis with those without and between patients with mild chondrocalcinosis with those with severe chondrocalcinosis.

Results

Chondrocalcinosis was found in 173 male patients (34%) undergoing TKAs during this period compared with 224 female patients (24%) (p < 0.001). The Knee Society scores for knee rating and function were similar in patients with or without chondrocalcinosis undergoing TKA. However, patients with visible CPPD deposition who underwent synovectomy for proliferative synovitis had diminished final ROM and Knee Society knee rating scores (107^o versus 115^o knee flexion, p < 0.001 and 87 versus 94 points, p = 0.001). We cannot determine whether this result is because of the synovectomy or severity of the disease, and therefore we cannot recommend a synovectomy at this time. Revision rates were no different among patients with chondrocalcinosis compared with those without it (3.6% versus 2.2%, p = 0.2).

Conclusions

Chondrocalcinosis is common among patients undergoing TKA for osteoarthritis. The presence of CPPD deposition does not appear to affect the ROM and Knee Society scores of patients with CPPD but without severe synovitis. However, patients with severe synovitis and visible CPPD who underwent thorough synovectomy may be at risk for having decreased postoperative ROM and pain develop.

Level of Evidence

Level III, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.

Introduction

Chondrocalcinosis and joint inflammation resulting from deposition of calcium crystals have been associated with various musculoskeletal disorders including osteoarthritis [1, 17]. Calcium pyrophosphate dihydrate (CPPD) deposits are frequent causes of chondrocalcinosis, a condition frequently seen on routine radiographic examinations of the knee [9]. CPPD crystals tend to form in articular tissues, and although in theory any joint may be affected, chondrocalcinosis is found most commonly in the knee, especially in the elderly, and it has been reported that up to 60% of patients undergoing TKAs will have evidence of it [2, 18].

The effect of chondrocalcinosis on patients undergoing TKA is unknown. A diagnosis of chondrocalcinosis carries potential implications for TKA because it is often polyarticular and may involve other joints, thereby perhaps affecting postoperative recovery [3]. Furthermore, surgery might precipitate attacks of pseudogout in the operative site resulting in significant joint inflammation and pain and sometimes mimic other signs and symptoms of joint infection [6, 7, 14]. Finally, to our knowledge, there are no reports outlining the clinical influence of chondrocalcinosis on pain or function among patients undergoing primary TKA.

Therefore, the purposes of this study are to (1) determine the prevalence of chondrocalcinosis in a large group of patients undergoing TKA for osteoarthritis; (2) evaluate the effect of CPPD crystal deposition in the arthritic knee on ROM and The Knee Society (KS) scores; (3) determine if patients with chondrocalcinosis and severe synovitis who underwent thorough synovectomy are at risk for lower postoperative KS scores and less ROM; and (4) assess if chondrocalcinosis is associated with increased rates of revision surgery.

Patients and Methods

We retrospectively reviewed the medical records of 1500 primary TKAs performed for knee osteoarthritis by one surgeon (PAL) at our institution between 1992 and 2003. The minimum followup was 2 years with an average followup of 57 months (range, 24–120 months). Complete clinical records were available for all patients for a minimum of 12 months. One hundred nineteen knees lacked the minimum 24-month clinical and radiographic data and were excluded from the final analysis. There were 934 females and 511 males with a mean age of 70 years (range, 34–100 years). Fifty-five patients underwent bilateral knee replacements. Inclusion criteria for this study included all patients older than 18 years undergoing primary TKA for end-stage arthritis of the knee. To capture the true prevalence of chondrocalcinosis in this population, no patient in this series was excluded from the final analysis. This study was approved and conducted according to the guidelines set by our institutional review board.

All surgeries were performed using a median parapatellar approach using cemented femoral and tibial components. Most patients underwent TKA using a posterior cruciate substituting knee system (n = 1350) (PFC^® knee prosthesis; Depuy, Warsaw IN, USA; and Scorpio^® knee system; Stryker Orthopaedics, Mahwah NJ, USA). All patients with chondrocalcinosis underwent knee replacement using a posterior stabilized implant. Intraoperatively, the presence of chondrocalcinosis was prospectively graded using a subjective, visual scale by the operating surgeon based on the amount of visible crystal deposits found at the time of surgery from 0 to 4: 0 = none, 1 = minimal, 2 = mild, 3 = moderate, and 4 = severe. All patients with moderate to severe chondrocalcinosis, visible crystal deposition, and proliferative synovitis underwent a thorough synovectomy in addition to primary TKA (n = 50) (Table 1). The synovium in the suprapatellar pouch, medial, and lateral gutters was sharply excised and separated from the joint capsule during knee exposure. After bony resections, the synovium from the posterior aspect of the knee was removed with a rongeur. Postoperatively, all patients received aspirin for 6 weeks for deep venous thrombosis prophylaxis.

Table 1.

Distribution of severity of visible crystal deposition in TKA

Grade	Total Knees	Males	Females	Synovectomy
1*	210	73	130	0
2*	153	75	69	0
3	33	30	3	33
4	17	16	1	17

* Totals exceed the sum of patient number because of bilateral procedures.

The patients were followed at regularly scheduled intervals and the clinical data were prospectively collected. All data and surveys were collected and administered by research assistants and prospectively entered in a clinical database. From the operative data, the prevalence of visible chondrocalcinosis in a group of patients undergoing primary TKAs was determined. Clinical outcomes were evaluated using The KS score for knee rating and function [8]. Comparisons of the clinical ratings and ROM were made between the groups of patients with and without chondrocalcinosis undergoing primary TKAs. Furthermore, the KS scores and final ROM of patients with high-grade chondrocalcinosis (Grades 3 and 4) who underwent synovectomy were compared with those of patients with lesser amounts of crystal deposition (Grades 1 and 2). Finally, the frequency of revision surgery was compared between patients with visible chondrocalcinosis compared with patients with no crystal deposits, including evidence of impending revision by radiographic evidence of loosening. Statistical analysis of continuous variables was conducted using paired and unpaired t-tests. Categorical variables such as the severity of chondrocalcinosis and risk for revision surgery were evaluated using the chi-square and Mann Whitney U tests (IBM SPSS Statistics 19.0; IBM, Armonk, NY, USA).

Results

Overall, chondrocalcinosis was present in 413 (27.5%) knees at the time of surgery. Men were more likely to have CPPD deposition at the time of surgery (34% versus 24%, p < 0.001) and have increased severity of chondrocalcinosis compared with women (median Grade 2 versus Grade 1, p < 0.001). There was no difference in the mean age between men and women in this series (71.5 versus 71.4 years, p = 0.61).

The presence of CPPD crystal deposition at the time of primary TKA was not associated with differences in postoperative ROM or KS score at the time of latest followup. Patients with chondrocalcinosis as a group had slightly better preoperative knee flexion compared with patients without chondrocalcinosis as a group (average, 109° [95% CI, 91^o–117^o] versus 106° [95% CI, 87^o–112^o], p = 0.02). However, postoperatively, there was no difference in knee flexion between the two groups. At last followup, the mean postoperative knee flexion averaged 113° (95% CI, 95^o–117^o) and 112° (95% CI, 89^o–119^o) in patients without chondrocalcinosis and those with chondrocalcinosis, respectively (p = 0.34) (Fig. 1). Before surgery, the mean KS score for knee rating was 43 points (95% CI, 31–50 points) for patients with chondrocalcinosis compared with 48 points (95% CI, 36–55 points) for patients without chondrocalcinosis (p = 0.25). After surgery, pain and functional scores improved equally and were similar in both groups. The average KS score for knee rating was 93 points (95% CI, 87–97 points) for patients with chondrocalcinosis compared with 94 points (95% CI, 87–95 points) for patients without visible chondrocalcinosis (p = 0.52) (Fig. 2). Similarly, the average KS function score averaged 68 points for patients with chondrocalcinosis (95% CI, 57–81 points) compared with 68 points for patients without chondrocalcinosis (95% CI, 59–75 points) (p = 0.60).

Fig. 1.

Patients with chondrocalcinosis as a group did not have significantly lower final knee flexion angles after TKA at a mean of 57 months followup compared with patients without chondrocalcinosis. CC = chondrocalcinosis.

Fig. 2.

Patients with chondrocalcinosis as a group did not have significantly lower final Knee Society (KS) knee rating scores after TKA compared with the control group. CC = chondrocalcinosis.

The amount of CPPD crystal deposits noted at the time of surgery affected KS knee rating scores and final knee flexion after primary TKA. Before surgery, there were no differences in the preoperative knee flexion (average, 104° [95% CI, 87^o–110^o] versus 106° [95% CI, 91^o–115^o], p = 0.27) or KS score for knee rating (average, 31 points (95% CI, 25–44 points) versus 36 points [95% CI, 25–45 points], p = 0.12) for patients with Grades 3 and 4 CPPD deposition compared with Grades 1 and 2 CPPD deposition. Postoperatively, reduced knee flexion was observed in patients with higher-grade CPPD crystal deposition treated with thorough synovectomy compared with patients with lower-grade CPPD crystal deposition. At last followup, the average knee flexion was 107° (95% CI, 97^o–111^o) compared with 115° (95% CI, 105^o–120^o) in patients with Grades 3 and 4 chondrocalcinosis and Grades 1 and 2 chondrocalcinosis respectively (p = 0.001). In addition, the final KS knee rating score was lower in patients treated with a thorough synovectomy, mainly reflecting the reduction in knee flexion (average, 87 points [95% CI, 83–91 points] versus 94 points [95% CI, 86–97 points], p = 0.001) (Table 2).

Table 2.

Range of motion and Knee Society scores

Variable	Grades 1–2	Grades 3–4	p value
Preoperative flexion (95% CI)	106 (91–115)	104 (87–110)	0.27
Postoperative Flexion (95% CI)	115 (105–120)	107 (97–111)	0.001
Preoperative Knee Society knee score (95% CI)	36 (25–45)	31 (25–44)	0.12
Postoperative Knee Society knee score (95% CI)	94 (86–97)	87 (83–91)	0.001
Postoperative Knee Society function score (95% CI)	69 (63–77)	65 (55–71)	0.37

Thirty-nine patients (2.6%) subsequently underwent revision TKA at a mean followup of 57 months. Fifteen knees (3.6 %) with CCPD deposition required revision compared with 24 knees (2.2 %) without CPPD deposition (p = 0.2). The average time to revision surgery was 50 months (range, 31–98 months) in patients with chondrocalcinosis compared with 46 months (range, 28–113 months) in patients without chondrocalcinosis (p = 0.68). The most common causes for revision were infection (n = 15), instability (n = 7), aseptic loosening (n = 10), periprosthetic fracture (n = 4), and stiffness (n = 3).

Discussion

Chondrocalcinosis and joint inflammation resulting from deposition of calcium crystals have been associated with various musculoskeletal conditions including osteoarthritis [1, 17]. Chondrocalcinosis frequently affects the knee, with some authors reporting evidence of crystal deposition in the knee in as much as 60% of patients undergoing TKA [2, 18]. The influence of chondrocalcinosis on the clinical outcome of primary TKA is unknown. Therefore, the purposes of this study were to: (1) determine the prevalence of chondrocalcinosis in a large group of patients undergoing TKA for osteoarthritis; (2) evaluate the effect of CPPD crystal deposition in the arthritic knee on ROM and the KS score; (3) determine if patients with chondrocalcinosis and severe synovitis who underwent thorough synovectomy are at risk for lower postoperative KS scores and less ROM; and (4) assess if chondrocalcinosis is associated with increased rates of revision surgery.

This study has several limitations. First, chondrocalcinosis and CCPD disease are radiographic and microscopic manifestations of crystal disease respectively and because no radiographic or fluid crystal analysis was performed, the true prevalence of chondrocalcinosis may be underestimated. Second, the severity of chondrocalcinosis was rated subjectively by one observer (PAL) from a scale of 0 to 4 and not based on a validated instrument, thus potentially introducing variability and bias. However, because all knees were graded by one observer, and the prospectively collected results were analyzed by comparing patients with mild crystal deposition (Grades 1 and 2) with patients with higher amounts of CPPD crystal deposits (Grades 3 and 4), the effect of variability and reproducibility of these subjective observations are minimized. Third, patients with severe visible chondrocalcinosis (Grades 3 and 4) underwent a thorough synovectomy at the time of the primary TKA. At last followup, these patients as a group had lower average knee flexion compared with patients with mild chondrocalcinosis (Grades 1 and 2) who underwent TKA. However, because there was no control group of patients with severe chondrocalcinosis who did not receive a thorough synovectomy as part of their surgical procedure, we have limited ability to make statements regarding whether the severity of crystal disease or the sequelae of synovectomy (ie, increased risks of bleeding, postoperative fibrosis and pain) contributed to these inferior outcomes. Finally, this is an observational study looking at the presence of CPPD deposits at the time of the primary TKA. Although chondrocalcinosis is known to be associated with the development of osteoarthritis, its role in the pathogenesis is unclear. Furthermore, not every patient with chondrocalcinosis will require a TKA. Consequently, evaluating the effect of CPPD crystal deposition disease on the subsequent KS scores, ROM, and revision rates of TKA is important and valuable.

Our results show that chondrocalcinosis is commonly found at the time of TKA. In our series, 413 (27.5%) patients undergoing TKAs had visible intraoperative findings consistent with CPPD crystal deposition, and the condition was more common in males. Terkeltaub also reported a high prevalence of crystal deposition in patients with osteoarthritic knees [15]. Derfus et al. [2] reported a positive correlation between synovial fluid crystal deposition and radiographic severity of knee arthritis. In a series of 53 knees undergoing TKAs, Derfus et al. reported CPPD or basic calcium phosphate crystals, identified microscopically, in the synovial fluid in 60% of patients but only 31% of patients had radiographic chondrocalcinosis [2]. Although the true incidence of chondrocalcinosis in this patient population is unknown, the diagnosis of acute pseudogout attack may need to be considered in patients with otherwise well-functioning TKAs who present with sudden onset of joint pain, swelling, and inflammation mimicking joint infection [11]. Consequently, visible calcium crystal deposition is commonly found in patients with arthritic knees undergoing TKA.

The presence of CPPD crystals at the time of knee surgery was not associated with decreased ultimate knee ROM or lower KS scores after surgery. The similarities of functional disabilities between patients with chondrocalcinosis as a group to those without chondrocalcinosis are consistent with other published reports [5, 16]. Viriyavejkul et al. [16] compared the characteristics of patients with and without CPPD undergoing TKA for osteoarthritis and reported no differences in age at pain onset, time to surgery, difficulty in performing daily functions, or history of prior joint inflammation. Additionally, they also reported a high prevalence of crystals found in the synovial fluid (53%) at the time of surgery. but did not report on functional outcomes after TKA [16]. However, given that the main predictor of postoperative ROM is preoperative and intraoperative ROM, and ROM [12, 13] and pain scores are the major determinants of The KS scoring system^© [8], it is consistent that patients with chondrocalcinosis would have similar clinical KS scores after TKA compared with patients without chondrocalcinosis.

In our study, a thorough synovectomy was associated with lower final knee flexion and lower KS scores in patients with chondrocalcinosis. Fifty patients with severe CPPD deposition (Grades 3 and 4) were treated with a thorough synovectomy at the time of the primary TKA. When comparing this subgroup of patients with patients with milder disease (Grades 1 and 2, n = 363) who were not treated with a thorough synovectomy, the final knee flexion (p = 0.001) and KS knee rating scores were significantly (p = 0.001) lower. Because we had no control group, we could not determine whether the reduced postoperative ROM and corresponding reduction in KS knee rating scores were the result of the severity of CPPD deposition or a complication of the synovectomy. Complete synovectomy can increase bleeding and recurrent hemarthrosis potentially leading to loss of ROM. Kilicarslan et al. [10] reported on a series of patients with noninflammatory arthritis randomized to TKA with complete synovectomy and without synovectomy. They found that although during the immediate postoperative period blood loss was greater in the synovectomy group, a complete synovectomy at the time of the TKA did not lead to differences in pain relief and eventual KS scores. Furthermore, Fuerst et al. [4] prospectively evaluated 100 patients with end-stage osteoarthritis undergoing TKA, looking at the effects of crystal deposits in the knee. Using various modes of analysis, they found that osteoarthritic cartilage was mineralized primarily with basic calcium phosphate and CPPD crystals and that the extent of mineralization correlated directly with the Hospital for Special Surgery knee scores. In our series, we also observed a trend for patients with Grades 3 and 4 CPPD crystal deposition to have lower KS pain scores compared with patients with Grades 1 and 2 disease (p = 0.12) preoperatively. Consequently, the extent and amount of visible CPPD crystal deposition and knee synovitis may affect knee function before TKA.

Finally, chondrocalcinosis did not affect the longevity of TKA in this series of patients. Our results show that at an average followup of 57 months, there were no differences in the revision rates between patients with chondrocalcinosis and without chondrocalcinosis (p = 0.2). Traditional mechanisms of failure including infection, instability, or aseptic loosening were no more prevalent in either group. There is little published information on the effect of chondrocalcinosis on TKA survivorship. Hernigou et al. [5] reported on a series of 234 unicompartmental knee arthroplasties and compared the failure rates of patients with and without chondrocalcinosis and found no differences in the 15-year cumulative survivorship of the implants. Therefore, CPPD crystal deposition is not a poor predictor for TKA survivorship.

Chondrocalcinosis and CPPD crystal deposition are common in patients undergoing primary TKA for osteoarthritis. As a group, the presence of chondrocalcinosis does not appear to influence ultimate knee flexion, KS knee rating and functional scores, or revision rates. In our series, patients with severe chondrocalcinosis treated with complete synovectomy at the time of primary TKA had lower knee flexion and inferior KS pain scores compared with patients with mild chondrocalcinosis treated without synovectomy. We cannot determine whether this result is the result of the synovectomy or severity of the disease, and therefore we cannot recommend a thorough synovectomy at this time.