Aging Clinical and Experimental Research

, Volume 30, Issue 4, pp 315–321 | Cite as

Profile of osteoarthritic patients undergoing hip or knee arthroplasty, a step toward a definition of the “need for surgery”

  • Audrey Neuprez
  • Arnaud H. Neuprez
  • William Kurth
  • Philippe Gillet
  • Olivier Bruyère
  • Jean-Yves Reginster
Original Article



The objective of this study is to characterize, based on clinical, radiographic, health-related, quality-of-life-related, and demographic variables, the profile of a large, homogeneous, cohort of patients undergoing knee or hip arthroplasty, in a public hospital. Current regulatory guidelines for structure-modifying agent are not clear regarding hard clinical endpoint. The “need for surgery” has been suggested as a potential relevant outcome, but, until now, it is poorly defined. By characterizing a large number of patients who undergo total hip or total knee replacement, this paper aims at providing a contribution to the better definition of the “need for surgery” in advanced OA of the lower limbs.


Consecutive patients who underwent primary knee arthroplasty (KA) or hip arthroplasty (HA) between December 2008 and February 2013, in an academic hospital, and who were diagnosed with hip or knee osteoarthritis (OA) (ACR criteria). Data collected at baseline included demographic and clinical data; Kellgren–Lawrence radiological grading; Western Ontario and Mc Master Universities Arthritis Index (WOMAC); EuroQol five dimensions questionnaire and EuroQol visual analog scale; and 36-item Short Form Health Survey.


626 subjects were included, 346 with hip OA and 280 with knee OA. Significant differences between subjects in need of an HA or of a KA were seen in terms of age (66.5 years versus 65 for hip), duration of complaints (2188 days versus 1146.5 for hip), BMI (28.68 kg/m² versus 27.07), radiological status (severe OA were found in 79.85% in knee group and 68.73% in hip group), comorbidities (FCI higher in knee group), traumatic of surgical history (37 versus 6%), and health-related quality of life and function (patients with HA had a poorer clinical status regarding WOMAC and WOMAC subscale).


Significant differences were observed between patients undergoing KA or HA. These differences might be useful to better understand the “need for surgery” status in these indications. This concept may help to define responders and failures to pharmacological treatment of OA.


Osteoarthritis Hip Knee Arthroplasty Treatment 


Osteoarthritis (OA) is the most prevalent musculoskeletal condition and a highly disabling disease, affecting up to an estimated 10% of men and 18% of women over 60 years, worldwide [1]. OA can be diagnosed by self-report, clinical presentation, or radiographic features. According to the definition used, the prevalence of the disease may substantially differ. When basing the diagnosis of OA on radiographs, hand is the most prevalent location, while hip is the less frequently affected joint. This was shown in both genders [2]. OA of the hip (HOA) and knee (KOA) tends to generate the greatest burden to the population (physical, psychological, and socioeconomic) as pain and stiffness in these large weight-bearing joints often lead to the need for surgical interventions [3].

In 2011–2012, symptomatic KOA was reported to affect 14 million people in the US [4], while the 2010 global age-standardized prevalence of KOA and HOA was calculated at 3.8 and 0.85%, respectively [5]. Of 291 conditions, HOA and KOA were ranked as the 11th highest contributor to global disability and the 38th highest in disability-adjusted life years (DALYs) [5]. KOA and HOA are associated with a growing economic burden on society in terms of both burden of illness and cost of illness, expected to reach between 1 and 2.5% of the gross domestic product (GDP) for Western Europe and North American countries [6].

Risk factors for KOA and HOA include genetic inheritance, age, ethnicity, nutritional factors, female gender, local mechanical factors, obesity, and previous joint injury [7].

Traditionally, the management of lower limbs OA involves a combination of treatment modalities, including non-pharmacological and pharmacological interventions [8, 9, 10], and joint arthroplasty (JA) is indicated for patients severely symptomatic, whose quality of life is poor, with end-stage disease and who are non-responsive to other therapeutic approaches [11, 12]. The number of hip (HA) and knee (KA) arthroplasties increased rapidly since 2000 in most Organisation for Economic Co-operation and Development (OECD) countries. On average, the rate of HA increased by about 35%, while the rate of KA nearly doubled in the OECD member countries between 2000 and 2013 [13]. In Belgium, the annual incidence of JA for primary OA is higher than the average for OECD countries. Out of 35 members states, in 2013, Belgium ranked 4th and 5th, for HA (246 per 100,000 inhabitants, average: 161) and KA (187 per 100,000 inhabitants, average: 121), respectively [13].

No chemical entity is currently approved by the European or North American regulatory agencies for the structural management of OA [10, 14]. At this time, agencies do not recommend the use of “time to surgery” as a primary endpoint of failure for structure-modifying trials of KOA or HOA because of bias by non-disease-related factors like patient willingness for surgery or economic factors [15, 16].

The objective of this study is to characterize, based on clinical, radiologic, economic, and socio-demographic variables, the profile of a large, homogeneous cohort of patients undergoing KA or HA, in a public hospital. A better understanding of the presentation of this population may help to better define the “need for surgery”, a concept which was suggested as a potential primary endpoint of failure for structure-modifying trials in KOA or HOA [15, 16]. The endorsement by the regulatory authorities of a consensual definition of the “need for surgery” as a validated outcome for pivotal studies would stimulate the development of new chemical entities in this indication, hence giving OA patients the opportunity to access medications which can prevent or delay the progression of OA and eventually reduce the number of needed JA.

Patients and methods

This study followed the principles of the Declaration of Helsinki. The local ethics committee approved this trial. Between December 2008 and February 2013, 845 consecutive patients with HOA or KOA (diagnosis based on the clinical and radiographic criteria of the American College of Rheumatology), aged 18 years of older, hospitalized for primary KA or HA in the Department of Orthopaedic Surgery of a single Belgian University hospital (public sector), were eligible for the study. The participants signed a fully informed consent. Exclusion criteria were surgery for indications other than OA, revision surgery, or lack of written consent. The day before the surgical procedure, patients received and completed, without external assistance, an extensive questionnaire. Responses were double checked (for missing data and misunderstandings) by two health care professionals, who were not part of the surgical management team. Baseline characteristics included age (years), gender, height (cm), weight (kg), and Body Mass Index (BMI—kg/m²). Duration of knee or hip complaints was recorded as well as any previous traumatic or surgical history of the lower limbs.

Comorbidities were recorded and summarized using the Functional Comorbidity Index (FCI) which consists of a list of 18 diagnoses, each being significantly associated with declining function. One point is assigned for the presence of each diagnosis, hence giving a global score between 0 and 18 [17]. The impact of OA on pain, function, and quality of life was assessed, using the Western Ontario and Mac Master Universities Osteoarthritis Questionnaire (WOMAC) and the Short Form 36 (SF-36) scale. The WOMAC includes 24 items covering three domains: pain, stiffness, and physical function and captures the level of each domain with five response categories using an ordinal scale. Lower values in the traditional scoring method (ranging from 0 to 96) reflect a better health status [18]. The generic health measure SF-36 is a validated questionnaire assessing health-related quality of life (HRQoL). It is a self-administrated 36-item questionnaire comprising eight health dimensions. Scoring ranges from 0 to 100 points, with higher scores representing better health. This tool also includes a separate variable assessing the perceived changes in overall health status compared to the status prevailing 1 year prior to the assessment [19]. The HRQoL was also assessed by two instruments developed by the EuroQol Group Association (EQ), the EuroQol Visual Analog Scale (EQ-VAS) and a generic tool assessing five dimensions (5D) of health: mobility, self-care, usual activity, pain/discomfort, and anxiety/depression (EQ-5D) [20].

X-rays of the target knee or hip (i.e., the joint that will be site of the TKA) (standing position) were obtained by routine analogic or digital technology and were transferred to the centralised radiology reading centre in Liege for reading and storage. X-rays were scored according to the Kellgren–Lawrence grading system (i.e., 0: no OA, 1: doubtful, 2: minimal, 3: moderate, and 4: severe). Scoring of X-rays was conducted by one single experienced physician [21].

Patient’s characteristics, presence of different comorbidities, pain, physical functioning, and HRQoL were analysed using descriptive statistics. For normality and homogeneity of data, the tests of Shapiro–Wilk and Levene were used and then justified non-parametric statistical analysis. Continuous variables are presented as median with interquartile ranges (IQR P25–P75). Categorical variables are presented as number and percentage. For the comparison between independent groups, in the case of continuous data, Mann–Whitney (two samples) was performed. Categorical variables were compared with the Chi-squared test. Data were analysed using STATISTICA, version 12, in a Windows environment. The level of statistical significance was set at p < 0.05 for all analyses.


Of the 845 eligible patients, 626 subjects fulfilled the inclusion criteria and were invited to complete the survey. Of these patients, 346 (55.27%) benefited from an HA [337 operated with THA and 9 with hip resurfacing arthroplasty (HRA)] and 280 (44.73%) received a KA [266 operated with TKA and 16 with unicompartmental arthroplasty (UKA)]. From the 219 who were not included in the study (123 HA, 96 KA), 153 patients were females (69.86%), 66 were males (30.14%), and the median age was 73 years. Reasons for non-inclusion were language problems or insufficient literacy (n = 26–11.87%), lack of consent (n = 161–73.52%), or reduced preoperative cognitive, sensory, or physical capacity (n = 32–14.61%). 6.43% of the patients (n = 18) recruited on the basis of their KA, previously presented with HA. 12.14% (n = 34) presented previously with contralateral KA. Conversely, 3.76% of the patients (n = 13) recruited on the basis of HA, presented previously with KA. 19.94% (n = 64) presented previously with contralateral HA.

Table 1 shows the baseline characteristics of the study population.

Table 1

Characteristics of patients at the time of hip or knee arthroplasty

Site of prosthesis

Knee (n = 280–44.73%)

Hip (n = 346–55.27%)

p value




Median (P25–P75)



Median (P25–P75)



p = 0.17















Age at the operation, years


66.5 (60–73)


65 (58–73)

p = 0.03



p = 0.24















Duration of complaints at the operation, days


2188 (1079–5470)


1146.5 (551–2869)

p < 0.0001



28.68 (26.12–32.41)


27.07 (24.16–30.42)

p < 0.0001

 Underweight (n = 5) and normal weight—BMI <25







p < 0.0001

 Overweight—BMI 25–29.9







p = 0.31

 Obesity—BMI ≥30







p < 0.0001

KL score, distribution





p < 0.0001








p = 0.22








p = 0.01








p < 0.0001








p < 0.0001



2 (2–3)


2 (2–3)

p = 0.03

Surgical or traumatic background







p < 0.0001

At the time of joint arthroplasty (JA), patients with KA were significantly older and heavier, they presented a longer duration of OA complaints and a higher number of comorbidities, and they were more prone to have experienced a previous surgical or traumatic episode of the operated joint. It may seem surprising that the FCI differs in both groups (p = 0.03), whereas the median is identical. This is related to the fact that non-parametric tests do not compare medians, but the distribution is different in both groups.

At the target knee, KL stages 2, 3, and 4 were found in 15.75, 68.86, and 10.99% of the KOA cases, while in HOA cases, the respective proportions were 24.45, 36.28, and 32.45%. Aggregated K–L grades of 3–4 (severe OA) were found in 79.85 and 68.73% in knee OA and hip OA cases, respectively (p < 0.001).

On the preoperative fullength X-ray of KA patients, the deformations in frontal plane (varus–valgus alignment) were sought. Varus thrust was present in 53.21% patients (n = 149) and valgus thrust in 17.14% patients (n = 48). The lower limb axis was normal in 4.29% patients (n = 12) and this information was not available (no preoperative fullength X-ray) for 25.36% patients (n = 71).

The assessment of HRQoL (Table 2) showed that at the time of JA, patients with HA had a poorer clinical status (WOMAC) compared to patients with KA, this difference been mainly driven by a significant difference in the function subscale. No significant differences were observed for the pain and stiffness WOMAC subscales, between KA and HA. In terms of HRQoL, the only significant difference observed, for all the SF-36 subscales relates to a higher worsening of perceived health, during the year before surgery, for patients undergoing KA compared to HA.

Table 2

Health status, clinical presentation, and HRQoL of patients at the time of HA or KA

Site of prosthesis



p value


Median (P25–P75)

Median (P25–P75)


70 (55–75)

65 (50–75)

p = 0.15


0.56 (0.24–0.66)

0.47 (0.22–0.66)

p = 0.26

WOMAC total (0–96)

52 (41–63)

56 (43–67)

p = 0.02

 Pain (0–20)

11 (9–13.5)

12 (9–14)

p = 0.21

 Stiffness (0–8)

5 (4–6)

5 (4–6)

p = 0.33

 Function (0–68)

38 (28.5–44.5)

40 (30–47)

p = 0.01


 Physical functioning (PF)

30 (15–50)

30 (10–50)

p = 0.33

 Physical role functioning (RP)

0 (0–50)

0 (0–50)

p = 0.28

 Emotional role functioning (RE)

33.33 (0–100)

33.33 (0–100)

p = 0.72

 Vitality (VT)

50 (35–60)

50 (35–60)

p = 0.39

 Mental health (MH)

62 (44–80)

64 (48–76)

p = 0.86

 Social role functioning (SF)

75 (50–87.5)

62.5 (50–87.5)

p = 0.56

 Bodily pain (BP)

33.75 (22.5–45)

32.5 (22.5–45)

p = 0.12

 General health perceptions (GH)

60 (50–75)

65 (45–75)

p = 0.64

 Health change

50 (25–50)

25 (25–50)

p = 0.002


This large prospective, single-centre, including 626 subjects was designed to better characterize the profile of patients, at the time of a hip or knee replacement. The objective was to contribute to a better definition of the “need for surgery” status, a concept which might subsequently be used as a primary endpoint in studies assessing structure-modifying drugs in OA.

We observed significant differences between subjects in need of an HA or of a KA in terms of age, duration of complaints, BMI, radiological status, comorbidities, traumatic of surgical history, HRQoL, and function.

In both KA and HA, we found a higher number of women compared to men. Whereas the F/M ratio was slightly higher in the HA than in the KA group, this difference did not reach the level of statistical significance. This observation is not surprising. Indeed, the incidence of knee, hip, and hand OA is known to be higher in women than in men. In women, it increases dramatically around the time of menopause at all sites [3]. Female gender was reported to be an independent risk factor for incidence of KOA and progression of HOA [22]. The proportion of women observed in our study (54% for KOA and 59% for HOA) is also consistent with a recent meta-analysis showing an odds ratio of 1.68 (95% CI 1.37–2.07) for females compared to males for OA of the lower limbs [23]. Women tend to have a more severe KOA, particularly after menopausal age. However, whereas the incidence rate of hip OA in men is reported to be lower, it is generally observed that males and females have no difference in the severity of HOA [24].

As expected, our population is overweighted or obese. Indeed, these conditions were consistently shown to increase the risk of OA of the lower limbs, and BMI is known to be a determinant factor in the incidence of both KOA and HOA, as well as in the progression and severity of HOA [22, 25]. It was suggested that up to 24.6% of new cases of knee pain/OA could be avoided if obesity and overweight are removed [23]. The greater proportion of overweight and obesity observed in our KA group compared to HA is consistent with a previous study which showed a greater association between excess weight and the development of KOA compared to HOA [26]. The mechanism trough which obesity influences the prevalence and progression of OA is still debated. Recent evidence suggests that the “old” mechanical hypothesis does not represent the only pathway through which obesity has a negative effect on OA. Inflammation is acknowledged as an important pathway in the development of knee OA [27]. White adipose tissue has been recognized as an important secretory organ of adipokines that play an important role in bone and cartilage homeostasis. The immunomodulatory effects of adipokines imply altered local but also systemic inflammation [28]. Recent findings suggest that healthy diet, such as Mediterranean diet, known to have anti-oxidant and anti-inflammatory properties may reduce the risk of knee OA [29].

Information on comorbidities was gathered using the FCI, a validated instrument developed specifically to objectively assess the preoperative status of patients undergoing joint replacement [30]. FCI of the HA group was significantly lower than in the KA group, which is consistent with previous studies showing that a higher number of comorbidities is usually found in patients with KA than in HA [31].

The effectiveness of HA and KA in relieving pain and improving function has been well documented with clinically important short and long-term improvements. JA is considered to be an effective and cost-effective treatment for patients with end-stage KOA and HOA who experience severe pain, activity limitation and for whom conservative treatment failed to improve the symptoms [9, 10, 32, 33].

Patients in our KA group were older and they experienced OA symptoms for longer than those undergoing HA. A hypothesis to explain this observation might be that patients and surgeons wait longer before deciding to operate for JA in the knee compared to the hip. This may be related to previous reports suggesting that revision or replacement of KA may occur earlier and more often than what is generally observed for HA [12, 34], even though contradictory publications exist [35]. Similarly, several authors have reported higher improvements in quality of life after HA compared to KA [36]. Therefore, a subjective fear of the outcomes of KA might be a conscious of unconscious driver to delay KA, whereas the overall positive perception of the short and long-term outcomes of HA could favour a quicker decision process for a surgical solution when facing severe HOA. Furthermore, the higher number of comorbidities and the higher BMI observed in our KA subjects could also explain a low propensity to choose surgery as an early option, these two conditions (i.e., excess weight and comorbidity) being linked to poorer post-operative outcomes [37].

One-third of the patients undergoing KA reported a previous history of joint injury or surgery of the target joint, while this prevalence is much lower in the HA group. In a recent review of thirteen cohort studies, an history of prevalent knee injury was shown to be the best single predictor of the occurrence of KOA (OR 2.83, 95% CI 1.91–4.19, compared to no previous injury) [23]. A previous joint injury was also identified as a significant risk factor for HOA, but to a lesser extends than for KOA [38].

In our sample, patients with KOA presented a greater radiologic severity (i.e., K–L score) than those with HOA. This might look surprising, since, in the literature, the majority of studies conclude that more severe radiographic OA preoperatively is associated with better outcomes in HA or KA. However, this evidence is less robust for KA [39, 40, 41, 42]. The greater radiographic severity may be simply linked to the greater age and longer duration of the disease in our KOA sample.

Our patients with HOA have poorer WOMAC score than KOA, a difference mainly driven by a more important functional impairment, the values for the WOMAC pain, and stiffness subscales being non-significantly different between the groups [43]. The observation that patients with KA have a greater radiographic severity but less functional disability may reflect a greater impact of hip integrity on patients’ ability to cope with the activities of daily living. Indeed, whereas knee is a major contributor to lower limbs stability when standing or walking, hip has a much greater mobility in all directions and is involved in many movements and functions, not limited to lower limbs but also involving the pelvis, the spin, and, in some cases, the upper body. Therefore, a relatively mild radiologic deterioration of the hip might be perceived by the patient as generating a greater loss of his/her functional capacity.

The only difference observed between KA and HA for the various dimensions of the SF-36 is a greater deterioration of HR-QOL during the year before surgery in patients with KOA, which is in accordance with general profile of our KA patients, suggesting that patients and surgeons wait until the patient reports a significant and rapid worsening of his/her well-being before considering TKA as an imminent therapeutic option.

The strength of our study is related to the size of our sample, the homogeneity of the cohort (i.e., all patients operated in the same department), and the public setting of the intervention (i.e., substantial intervention of the National Health System in the coverage of the expenses), all parameters mitigating the non-medical determinants of the decision to undergo JA, hence giving a somehow accurate picture of the medical profile of HOA and KOA patients in need for surgery. Moreover, the recruitment lasted 4 years only, precluding changes in the indications and techniques of surgical interventions.

At conversely, our study being conducted in one single centre, with a specific recruitment can hardly be extrapolated to other settings (private hospital, population with other genetics background, other dietary habits, etc). Our population is highly homogeneous and can hardly be extrapolated to all other developed countries. We know also that there are significant differences in waiting time for surgical procedures taking into account social, geographical, and health-system factors [44].

The comparison of these two groups could be biased by the presence of knee or hip OA, because people affected by knee OA could have hip OA and vice versa. It has already been mentioned in the literature that joint arthroplasty was often necessary in the remaining joints. The need for the second TJA may be due to the natural progression of a normal joint to an osteoarthritic one, or the worsening of pre-existing osteoarthritis. Furthermore, osteoarthritis is a multiarticular disease with disease progression most frequently observed in the contralateral joint [45, 46]. However, the impact of this potential bias is limited by the limited number of patients involved.

Lower limb deformity (varus or valgus) has been shown to be associated with an increase (fourfold regarding varus) in the risk of knee osteoarthritis progression [47]. Our results confirmed the clinical belief that varus thrust is more common than valgus thrust. It will be interesting to study later the profile of patients with these deformities to evaluate whether their osteoarthritis started earlier or that the age at the time of surgery is earlier. This could argue for a more rapid clinical deterioration. Our study being planned for a duration of 5 years, and it will be of interest to compare the rate of progression of OA in patients with a substantial varus or valgus compare to the rest of the other population.


Our study, conducted in a large, homogeneous cohort of patients undergoing JA in a public setting, shows significant differences between patients at the time of KA and HA. These differences might be useful to better characterize the profile of patients “in need of” HA or KA, a concept for which, so far, an unequivocal consensual definition does not exist, but which, if further studies overcome this hurdle, could help to identify new primary endpoints for studies aiming at the development of structure-modifying drugs in OA. On the other hand, the possibility of predicting an individual risk of “need for surgery” in the years to come, as it has been done in osteoporosis for the FRAX algorithm, which predicts the individual fracture risk in both genders, for the next 10 years, could be useful. Nevertheless, it is necessary to have a very large population. It would be interesting to create a clinical consortium that would collect a large number of cohorts to identify the respective roles of the different risk factors and produce an algorithm similar to FRAX.


Compliance with ethical standards

Conflict of interest

On behalf of all authors, the corresponding author states that there is no conflict of interest.

Ethical approval

The local ethics committee approved this trial.

Informed consent

Informed consent was obtained from all individual participants included in the study.

Supplementary material

40520_2017_780_MOESM1_ESM.xlsx (108 kb)
Supplementary material 1 (XLSX 108 KB)


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Copyright information

© Springer International Publishing Switzerland 2017

Authors and Affiliations

  • Audrey Neuprez
    • 1
    • 2
    • 3
  • Arnaud H. Neuprez
    • 1
  • William Kurth
    • 2
  • Philippe Gillet
    • 2
  • Olivier Bruyère
    • 1
  • Jean-Yves Reginster
    • 1
  1. 1.Department of Public Health, Epidemiology and Health EconomicsUniversity of LiègeLiègeBelgium
  2. 2.Orthopaedic Surgery DepartmentUniversity Hospital of LiègeLiègeBelgium
  3. 3.Rehabilitation and Sports Traumatology DepartmentUniversity Hospital of LiègeLiègeBelgium

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