Free Bone Cement Fragments Leading to a Locked Knee 3 Years after Medial Unicompartmental Knee Arthroplasty: A Case Report



Michelangelo Palco, MD1; Roberto Caminiti, MD2; Filippo Familiari, MD3; Roberto Simonetta, MD2

Perm J 2021;25:20.318
E-pub: 05/19/2021

Unicompartmental knee arthroplasty (UKA) is a reliable alternative to total knee arthroplasty (TKA) in patients with isolated medial knee osteoarthritis. UKA provides a lot of potential advantages over TKA and is related to less overall morbidity and mortality compared with TKA. Rare complications are limitation of knee movement and a clicking sensation associated with cement extrusion, both after UKA and TKA. In this report, we describe a patient who required arthroscopic removal of free bone cement fragments 3 years after a minimally invasive UKA.


In patients with isolated medial knee osteoarthritis (OA), unicompartmental knee arthroplasty (UKA) is a reliable alternative to total knee arthroplasty (TKA).1 UKA provides a lot of potential advantages over TKA, such as a less invasive approach, storage of native bone stock, retention of cruciate ligaments, lower perioperative morbidity, fester recovery, and greater patient satisfaction.2-4 Moreover, UKA is related to less overall morbidity and mortality compared with TKA.3

Aseptic loosening, polyethylene wear, periprosthetic fractures, OA progression on the contralateral compartment, infection, and hemarthrosis are described as rare complications after UKA.5-8 Pain, limitation of knee movement, and clicking sensations associated with cement extrusion are even more rare complications, both after TKA and UKA.9-13 These symptoms are usually caused by free bone cement fragments, and it has been reported that removing these fragments leads to complete symptom resolution in most cases.9-11,13

Here we report a patient with 2 free bone cement fragments that became symptomatic 3 years after medial UKA and who underwent successful arthroscopic removal.


An 81-year-old man, who was a master athlete (triathlon) with isolated medial compartment OA of the right knee, a preoperative range of motion (ROM) of 0 to 95°, and an amendable varus deformity of 5° underwent a UKA in September 2016. A cemented Oxford UKA (Biomet, Swindon, UK) was implanted through a minimally invasive approach. The postoperative period was uneventful, and the patient was discharged from the hospital after 2 days. Eight weeks after the surgery, the patient showed complete comfort and absence of medial knee pain, and he had an ROM of 0 to 120°. He concluded his supervised rehabilitation program 4 months after surgery. Afterward, the patient was followed on a yearly basis. At the 3-year follow-up examination, the patient presented with impossible active extension of the knee, a ROM of 10 to 100°, acute pain in the posterolateral aspect of the right knee, and reasonable swelling. An associated clicking sensation was present. Radiographs revealed 2 free bone cement fragments, 1 lying adjacent to the lateral femoral condyle and 1 engaged in the intercondylar notch. A comparison of the new and old radiographs proved these were new fragments (Figure 1). The patient consented to undergo arthroscopic removal of the free bone cement fragments (Figure 2). After a standard diagnostic arthroscopy using 2 standard (anterolateral and anteromedial) portals, the 2 fragments were removed using a grasping forceps (Figure 3). Postoperative radiographs showed complete removal of the bone fragments (Figure 4). At the 7-day follow-up examination, the patient had a complete relief from pain and was free from any discomfort. At the 1-year follow-up examination, the patient was pain free and had full ROM (Table 1).


Figure 1. (A and B) Postoperative radiographs. (C) New radiograph at the 3-year follow-up (anteroposterior view). * = femoral and tibial prosthesis components; white arrow = polyethylene component; black arrows = free bone cement fragments. (D) New radiograph at 3-year follow-up (lateral view). * = femoral and tibial prosthesis components; black arrows = free bone cement fragment adjacent to the lateral femoral condyle; white arrow = free bone cement fragment engaged in the intercondylar notch. (E) New radiograph at 3-year follow-up (60° Merchant view). * = femoral and tibial prosthesis components; black arrows = free bone cement fragment.


Figure 2. (A) Free bone fragment adjacent to the lateral femoral condyle. (B) Free bone fragment engaged in the intercondylar notch. White * = femoral prosthesis component; black * = polyethylene component; black arrow = free bone cement fragment; white arrow = grasping forceps. (C) Standard arthroscopic portals anterolateral and anteromedial, and previous minimally invasive approach.


Figure 3. Removed free bone cement fragments.


Figure 4. Radiograph in anteroposterior and lateral view after arthroscopic removal of free bone fragments.

Table 1. Timeline of relevant past medical history and interventions for an 81-year-old master triathlon athlete with a medical history negative for any disease and isolated medial compartment osteoarthritis

Date Summaries from initial and follow-up visits Diagnostic testing Interventions
September 2016 Knee pain and restriction of ROM Radiographs of the knee Implant of UKA
November 2016 Follow-up visits Radiographs of the knee Follow-on rehabilitation program until 4 mo after surgery
 •Absence of knee medial pain
 •ROM, 0–120°
November 2017 Follow-up visits
October 2018 Follow-up visits
October 2019 Follow-up visits Radiographs of the knee Arthroscopic removal of free bone cement fragments
 •ROM, 10–100°
 •Knee pain
 •Knee effusion
 •Clicking sensation
November 2019 Follow-up visits
 •No pain
 •ROM, 0–120°
October 2020 Follow-up visits
 •No pain
 •ROM, 0–120°

ROM = range of motion; UKA = unicompartmental knee arthroplasty.


Compared to TKA, UKA performed using a minimally invasive approach is a fairly new and very encouraging option for the treatment of isolated medial compartment OA of the knee. Strict inclusion criteria are necessary for patient selection, including no central pivot lesions, minimal or absent damage to the lateral compartment, correctable varus deformity, and a flexion deformity of less than 10°. Nevertheless, the choice of UKA has become popular because of several benefits, such as reduced hospitalization time, inferior postoperative pain, greater ROM, and rapid mobilization.14 Aseptic loosening continues to be the first reason for revision. In 1988, Goodfellow et al15 wrote about aseptic loosening (6.6% of incidence) as the cause of revision. In recent literature,16 the most frequent reason for UKA failure was aseptic loosening (36%), followed by OA progression (20%), recurrent pain (11%), instability (6%), infection (5%), and polyethylene wear (4%). Outcome is usually influenced by implant design, surgeon experience, and patient selection.17,18 The minimally invasive approach used to implant a UKA is a particular disadvantage for the reduced intraoperative field of vision of the posterior areas of the knee.11 Cementing is essential for survival of the implant; being afraid of oversighting excess cement or free bone cement fragments in this area might create a tendency in surgeons to cement inadequately.19-21 One case of UKA revision surgery to remove restrained cement was reported by Berger et al.22 The use of arthroscopy for the treatment of complications of TKA has been documented in previous studies.23 The removal of foreign bodies using arthroscopy has been associated with good results.24 In our case, arthroscopy confirmed to be an efficient procedure that was related to quick functional recovery and no major complications. Standard portals were used, and the procedure was not technically difficult. It is important to note that close attention must be paid to establish the position of the anteromedial and anterolateral portals so as not to damage the UKA. It is possible to use additional portals not to stress the knee, considering the presence of the UKA, but in our case this was not necessary. The chance of infection in patients treated with knee arthroscopy after TKA or UKA is described as rare (0%–3.7%)25-32 Lovro et al33 recently showed their long-term results (mean follow-up, 5.45 ± 2.5 years) in 762 patients. They reported that the incidence of revision for infection in patients who underwent ipsilateral knee arthroscopy after TKA was 6.3% compared to 2.2% of patients who underwent a TKA and did not undergo any knee arthroscopy procedure afterward.

This case emphasizes a possible complication when using a minimally invasive technique. We encourage the evaluation of the possibilities of polyethylene failure, loosening of any component, infection, or contralateral compartment disease before proceeding with an arthroscopic procedure. Free bone cement fragments are a sporadic and unknown complication of both UKA and TKA. To avoid them, the use of an adequate quantity of cement on both the components and the bone is suggested. It is recommended one pay close attention and examine the components after they have been implanted. For these reasons, we use a dental mirror to inspect the posterior aspect of the implant and a custom-made hook to remove excess cement. Last, it must be emphasized that the removal of pieces of ejected cement from behind the tibial component may cause the loosening of more cement fragments; therefore, it is recommended one remove only very large, fixed fragments or grossly loose cement. Howe et al11 noted that this complication may be helped by considering the size of the tibial component. The use of thinner polyethylene components usually occurs with minor bone removal and provides a small space in which to work, thus impairing vision and passing of instruments into the posterior aspect of the knee. Despite these issues, we prefer, whenever indicated, to use a thinner (7-mm) polyethylene insert.


The risk of encountering free bone cement fragments with a minimally invasive approach and is possible. A sufficient cement layer needs to be distributed and all surplus cement needs to be aspirated. We recommend using a special hook or dental mirror to remove residual cement. The use of arthroscopy has to be considered for treatment in patients with signs such as acute mechanical symptoms, effusion, or radiographic findings compatible with the presence of free bone cement fragments.

Disclosure Statement

The author(s) have no conflicts of interest to disclose.

Financial Support

No financial support was required for this work.

Author Affiliations

1Department of Biomedical, Dental and Morphological and Functional Images, Section of Orthopaedic and Traumatology, University of Messina, Messina, Italy

2Department of Orthopaedic and Traumatology, Casa di Cura Caminiti, Villa San Giovanni, Italy

3Department of Orthopaedic and Traumatology, Villa del Sole Clinic, Catanzaro, Italy

Corresponding Author

Michelangelo Palco, MD (

Author Contributions

Michelangelo Palco, MD, wrote the article, proposed the topic of the manuscript, and participated in submitting the final. manuscript. Roberto Caminiti, MD, participated in the critical review of the manuscript. Filippo Familiari, MD, reviewed the final manuscript. Roberto Simonetta, MD, coordinated the other authors. All authors have given final approval to the manuscript.


1. Beard DJ, Davies LJ, Cook JA, et al. The clinical and cost-effectiveness of total versus partial knee replacement in patients with medial compartment osteoarthritis (TOPKAT): 5-Year outcomes of a randomised controlled trial. Lancet 2019 Aug;394(10200):746–56. DOI:, PMID:31326135.

2. Lim JW, Cousins GR, Clift BA, Ridley D, Johnston LR. Oxford unicompartmental knee arthroplasty versus age and gender matched total knee arthroplasty: Functional outcome and survivorship analysis. J Arthroplasty 2014 Sep;29(9):1779–83. DOI:, PMID:24805827.

3. Lombardi AV, Berend KR, Walter CA, Aziz-Jacobo J, Cheney NA. Is recovery faster for mobile-bearing unicompartmental than total knee arthroplasty? Clin Orthop Rel Res 2009 Jun;467(6):1450–7. DOI:, PMID:19225852.

4. Lyons MC, MacDonald SJ, Somerville LE, Naudie DD, McCalden RW. Unicompartmental versus total knee arthroplasty database analysis: Is there a winner? Clin Orthop Rel Res 2012 Jan;470(1):84–90. DOI:, PMID:22038173.

5. Pandit H, Murray DW, Dodd CA, et al. Medial tibial plateau fracture and the Oxford unicompartmental knee. Orthopedics 2007 May;30(5 Suppl):28, PMID:17549863.

6. Aleto TJ, Berend ME, Ritter MA, Faris PM, Meneghini RM. Early failure of unicompartmental knee arthroplasty leading to revision. J Arthroplasty 2008 Feb;23(2):159–63. DOI:, PMID:18280406.

7. Goodfellow J, O’Connor J, Murray DW. The Oxford meniscal unicompartmental knee. J Knee Surg 2002 Fall;15(4):240–6, PMID:12416907.

8. Maheshwari R, Kelley SP, Langkamer VG, Loveday E. Spontaneous recurrent haemarthrosis following unicompartmental knee arthroplasty and its successful treatment by coil embolisation. Knee 2004 Oct;11(5):413–5. DOI:, PMID:15351420.

9. Kim WY, Shafi M, Kim YY, Kim JY, Cho YK, Han CW. Posteromedial compartment cement extrusion after unicompartmental knee arthroplasty treated by arthroscopy: A case report. Knee Surg Sports Traumatol Arthrosc 2006 Jan;14(1):46–9. DOI:, PMID:15875159.

10. Otani T, Fujii K, Ozawa M, et al. Impingement after total knee arthroplasty caused by cement extrusion and proximal tibiofibular instability. J Arthroplasty 1998 Aug;13(5):589–91. DOI: https://doi.org10.1016/s0883-5403(98)90061-4, PMID:9726327.

11. Howe DJ, Taunton OD, Engh GA. Retained cement after unicondylar knee arthroplasty. J Bone Joint Surg 2004 Oct;86(10):2283–6. DOI: https://doi.org10.2106/00004623-200410000-00022

12. Langkamer VG. Local vascular complications after knee replacement: A review with illustrative case reports. Knee 2001 Dec;8(4):259–64. DOI:, PMID:11706687.

13. Jung KA, Lee SC, Song MB. Lateral meniscus and lateral femoral condyle cartilage injury by retained cement after medial unicondylar knee arthroplasty. J Arthroplasty 2008 Oct;23(7):1086–9. DOI:, PMID:18534478.

14. Karataglis D, Agathangelidis F, Papadopoulos P, Petsatodis G, Christodoulou A. Arthroscopic removal of impinging cement after unicompartmental knee arthroplasty. Hippokratia 2012 Jan;16(1):76–9, PMID:23930064.

15. Goodfellow JW, Kershaw CJ, Benson MK, O’Connor JJ. The Oxford knee for unicompartmental osteoarthritis: The first 103 cases. J Bone Joint Surg Br 1988 Nov;70(5):692–701. DOI:, PMID:3192563.

16. van der List JP, Zuiderbaan HA, Pearle AD. Why do medial unicompartmental knee arthroplasties fail today? J Arthroplasty 2016 May;31(5):1016–21. DOI:, PMID:26725134.

17. Ackroyd CE. Medial compartment arthroplasty of the knee. J Bone Joint Surg Br 2003 Sep;85(7):937–42. DOI:, PMID:14516022.

18. Stern SH, Becker MW, Insall JN. Unicondylar knee arthroplasty: An evaluation of selection criteria. Clin Orthop Rel Res 1993 Jan;286:143–8. DOI:, PMID:8425335.

19. Ritter MA, Herbst SA, Keating EM, Faris PM. Radiolucency at the bone–cement interface in total knee replacement: The effects of bone-surface preparation and cement technique. J Bone Joint Surg 1994 Jan;76(1):60–5. DOI:

20. Smith S, Naima VSN, Freeman MAR. The natural history of tibial radiolucent lines in a proximally cemented stemmed total knee arthroplasty. J Arthroplasty 1999 Jan;14(1):3–8. DOI:

21. Walker PS, Soudry M, Ewald FC, McVickar H. Control of cement penetration in total knee arthroplasty. Clin Orthop Rel Res 1984 May;185:155–64. DOI:

22. Berger RA, Nedeff DD, Barden RM, et al. Unicompartmental knee arthroplasty. Clinical experience at 6- to10-year follow up. Clin Orthop Rel Res 1999 Oct;367:50–60. DOI:

23. Bocell JR, Thorpe CD, Tullos HS. Arthroscopic treatment of symptomatic total knee arthroplasty. Clin Orthop Rel Res 1991 Oct;271:125–34. DOI:

24. Gulan G, Jurdana H, Legović D, et al. Arthroscopic removal of metal foreign bodies from the knee joint after explosive war injuries. Coll Antropol 2009 Sep;33(3):907–9, PMID:19860123.

25. Hurst JM, Ranieri R, Berend KR, Morris MJ, Adams JB, Lombardi AV. Outcomes after arthroscopic evaluation of patients with painful medial unicompartmental knee arthroplasty. J Arthroplasty 2018 Oct;33(10):3268–72. DOI:, PMID:29980421.

26. Jerosch J, Aldawoudy AM. Arthroscopic treatment of patients with moderate arthrofibrosis after total knee replacement. Knee Surg Sports Traumatol Arthrosc 2007 Jan;15(1):71–7. DOI:, PMID:16710728.

27. Koh YG, Kim SJ, Chun YM, Kim YC, Park YS. Arthroscopic treatment of patellofemoral soft tissue impingement after posterior stabilized total knee arthroplasty. Knee 2008 Jan;15(1):36–9. DOI:, PMID:17897831.

28. Sekiya H. Painful knee is not uncommon after total knee arthroplasty and can be treated by arthroscopic debridement. Open Orthop J 2017 Oct;11:1147–53. DOI:, PMID:29290850.

29. Volchenko E, Schwarzman G, Robinson M, Chmell SJ, Gonzalez MH. Arthroscopic lysis of adhesions with manipulation under anesthesia versus manipulation alone in the treatment of arthrofibrosis after TKA: A matched cohort study. Orthopedics 2019 May;42(3):163–7. DOI:, PMID:31099882.

30. Wong J, Yau P, Chiu P. Arthroscopic treatment of patellar symptoms in posterior stabilized total knee replacement. Int Orthop 2002 Aug;26(4):250–2. DOI:

31. Diduch DR, Scuderi GR, Scott WN, Insall JN, Kelly MA. The efficacy of arthroscopy following total knee replacement. Arthroscopy 1997 Apr;13(2):166–71. DOI:, PMID:9127073.

32. Klinger HM, Baums MH, Spahn G, Ernstberger T. A study of effectiveness of knee arthroscopy after knee arthroplasty. Arthroscopy 2005 Jun;21(6):731–8. DOI:, PMID:15944632.

33. Lovro LR, Kang HP, Bolia IK, Homere A, Weber AE, Heckmann N. Knee arthroscopy after total knee arthroplasty: Not a benign procedure. J Arthroplasty 2020 Dec;35(12):3575–80. DOI:, PMID:32758379.

Keywords: arthroscopic, case report, cement, knee, locked, minimally invasive, UKA


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